diff --git a/utils/bazel/.bazelrc b/utils/bazel/.bazelrc
--- a/utils/bazel/.bazelrc
+++ b/utils/bazel/.bazelrc
@@ -35,15 +35,15 @@
 build:generic_clang --cxxopt=-std=c++14 --host_cxxopt=-std=c++14
 
 # Use `-Wall` and `-Werror` for Clang.
-build:generic_clang --copt=-Wall --copt=-Werror --host_copt=-Wall --host_copt=-Werror
+build:generic_clang --cxxopt=-Wall --cxxopt=-Werror
 
 # The Clang available on MacOS has a warning that isn't clean on MLIR code. The
 # warning doesn't show up with more recent Clangs, so just disable for now.
-build:generic_clang --cxxopt=-Wno-range-loop-analysis --host_cxxopt=-Wno-range-loop-analysis
+build:generic_clang --cxxopt=-Wno-range-loop-analysis
 
 # Build errors are not a helpful way to enforce deprecation in-repo and it is
 # not the point of the Bazel build to catch usage of deprecated APIs.
-build:generic_clang --copt=-Wno-deprecated --host_copt=-Wno-deprecated
+build:generic_clang --cxxopt=-Wno-deprecated
 
 ###############################################################################
 # Options for "generic_gcc" builds: these options should generally apply to
@@ -61,7 +61,7 @@
 
 # Build errors are not a helpful way to enforce deprecation in-repo and it is
 # not the point of the Bazel build to catch usage of deprecated APIs.
-build:generic_gcc --copt=-Wno-deprecated --host_copt=-Wno-deprecated
+build:generic_gcc --cxxopt=-Wno-deprecated
 
 # Disable GCC warnings that are noisy and/or false positives on LLVM code.
 # These need to be global as some code triggering these is in header files.
@@ -72,7 +72,7 @@
 build:generic_gcc --copt=-Wno-misleading-indentation --host_copt=-Wno-misleading-indentation
 
 # Use `-Werror` for GCC to make sure warnings don't slip past.
-build:generic_gcc --copt=-Werror --host_copt=-Werror
+build:generic_gcc --cxxopt=-Werror
 
 ###############################################################################
 # Generic Windows flags common to both MSVC and Clang.
diff --git a/utils/bazel/WORKSPACE b/utils/bazel/WORKSPACE
--- a/utils/bazel/WORKSPACE
+++ b/utils/bazel/WORKSPACE
@@ -4,6 +4,7 @@
 
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
+load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
 
 SKYLIB_VERSION = "1.0.3"
 
@@ -71,16 +72,43 @@
     name = "vulkan_sdk",
 )
 
-http_archive(
+git_repository(
     name = "bazel_toolchains",
-    sha256 = "1adf5db506a7e3c465a26988514cfc3971af6d5b3c2218925cd6e71ee443fc3f",
-    strip_prefix = "bazel-toolchains-4.0.0",
+    tag = "4.0.0",
+    remote = "https://github.com/bazelbuild/bazel-toolchains.git"
+)
+
+git_repository(
+    name = "rules_foreign_cc",
+    tag = "0.7.1",
+    remote = "https://github.com/bazelbuild/rules_foreign_cc.git"
+)
+
+load("@rules_foreign_cc//foreign_cc:repositories.bzl", "rules_foreign_cc_dependencies")
+
+rules_foreign_cc_dependencies()
+
+maybe(
+    http_archive,
+    name = "gmp",
+    build_file = "@llvm-raw//utils/bazel/third_party_build:gmp.BUILD",
+    sha256 = "fd4829912cddd12f84181c3451cc752be224643e87fac497b69edddadc49b4f2",
+    strip_prefix = "gmp-6.2.1",
     urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/releases/download/4.0.0/bazel-toolchains-4.0.0.tar.gz",
-        "https://github.com/bazelbuild/bazel-toolchains/releases/download/4.0.0/bazel-toolchains-4.0.0.tar.gz",
+        "https://gmplib.org/download/gmp/gmp-6.2.1.tar.xz",
+        "https://ftp.gnu.org/gnu/gmp/gmp-6.2.1.tar.xz",
     ],
 )
 
+maybe(
+    http_archive,
+    name = "mpfr",
+    build_file = "@llvm-raw//utils/bazel/third_party_build:mpfr.BUILD",
+    sha256 = "3127fe813218f3a1f0adf4e8899de23df33b4cf4b4b3831a5314f78e65ffa2d6",
+    strip_prefix = "mpfr-4.1.0",
+    urls = ["https://www.mpfr.org/mpfr-current/mpfr-4.1.0.tar.gz"],
+)
+
 load("@bazel_toolchains//rules:rbe_repo.bzl", "rbe_autoconfig")
 
 rbe_autoconfig(name = "rbe_default")
diff --git a/utils/bazel/llvm-project-overlay/libc/test/libc_test_rules.bzl b/utils/bazel/llvm-project-overlay/libc/test/libc_test_rules.bzl
new file mode 100644
--- /dev/null
+++ b/utils/bazel/llvm-project-overlay/libc/test/libc_test_rules.bzl
@@ -0,0 +1,32 @@
+"""LLVM libc starlark rules for tests."""
+
+load("@llvm-project//libc:libc_build_rules.bzl", "INTERNAL_SUFFIX")
+
+def libc_test(name, srcs, libc_function_deps, additional_deps = None, **kw):
+    """Add target for a libc test.
+
+    Args:
+      name: Test target name
+      srcs: List of sources for the test.
+      libc_function_deps: List of libc_function targets used by this test.
+      additional_deps: List of additional targets used by this test.
+      **kw: Attributes relevant for a cc_test. For example, name, srcs, deps.
+    """
+    if "deps" in kw:
+        fail("A libc_test target should list 'libc_function_deps' and " +
+             "'additional_deps' instead of 'deps'.")
+    deps = [
+        "@llvm-project//libc:libc_root",
+        "@llvm-project//libc/utils/UnitTest:LibcUnitTest",
+    ]
+    for d in libc_function_deps:
+        deps.append(d + INTERNAL_SUFFIX)
+    if additional_deps:
+        deps.extend(additional_deps)
+    native.cc_test(
+        name = name,
+        srcs = srcs,
+        deps = deps,
+        features = ["-link_llvmlibc"],  # Do not link libllvmlibc.a
+        **kw
+    )
diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/fenv/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/src/fenv/BUILD.bazel
new file mode 100644
--- /dev/null
+++ b/utils/bazel/llvm-project-overlay/libc/test/src/fenv/BUILD.bazel
@@ -0,0 +1,102 @@
+# Tests for LLVM libc math.h functions.
+
+load("@llvm-project//libc:test/libc_test_rules.bzl", "libc_test")
+
+licenses(["notice"])
+
+libc_test(
+    name = "exception_status_test",
+    srcs = ["exception_status_test.cpp"],
+    additional_deps = ["@llvm-project//libc:__support_fputil"],
+    libc_function_deps = [
+        "@llvm-project//libc:feclearexcept",
+        "@llvm-project//libc:feraiseexcept",
+        "@llvm-project//libc:fetestexcept",
+    ],
+)
+
+libc_test(
+    name = "rounding_mode_test",
+    srcs = ["rounding_mode_test.cpp"],
+    libc_function_deps = [
+        "@llvm-project//libc:fegetround",
+        "@llvm-project//libc:fesetround",
+    ],
+)
+
+libc_test(
+    name = "enabled_exceptions_test",
+    srcs = ["enabled_exceptions_test.cpp"],
+    additional_deps = [
+        "@llvm-project//libc/utils/UnitTest:fp_test_helpers",
+        "@llvm-project//libc:__support_common",
+        "@llvm-project//libc:__support_fputil",
+    ],
+    libc_function_deps = [
+        "@llvm-project//libc:feclearexcept",
+        "@llvm-project//libc:feraiseexcept",
+        "@llvm-project//libc:fetestexcept",
+    ],
+    tags = ["nosan"],
+)
+
+libc_test(
+    name = "feholdexcept_test",
+    srcs = ["feholdexcept_test.cpp"],
+    additional_deps = [
+        "@llvm-project//libc/utils/UnitTest:fp_test_helpers",
+        "@llvm-project//libc:__support_common",
+        "@llvm-project//libc:__support_fputil",
+    ],
+    libc_function_deps = ["@llvm-project//libc:feholdexcept"],
+    tags = ["nosan"],
+)
+
+libc_test(
+    name = "exception_flags_test",
+    srcs = ["exception_flags_test.cpp"],
+    additional_deps = [
+        "@llvm-project//libc:__support_fputil",
+    ],
+    libc_function_deps = [
+        "@llvm-project//libc:fegetexceptflag",
+        "@llvm-project//libc:fesetexceptflag",
+    ],
+)
+
+libc_test(
+    name = "feclearexcept_test",
+    srcs = ["feclearexcept_test.cpp"],
+    additional_deps = ["@llvm-project//libc:__support_fputil"],
+    libc_function_deps = ["@llvm-project//libc:feclearexcept"],
+)
+
+libc_test(
+    name = "feenableexcept_test",
+    srcs = ["feenableexcept_test.cpp"],
+    additional_deps = ["@llvm-project//libc:__support_common"],
+    libc_function_deps = [
+        "@llvm-project//libc:fedisableexcept",
+        "@llvm-project//libc:feenableexcept",
+        "@llvm-project//libc:fegetexcept",
+    ],
+)
+
+libc_test(
+    name = "feupdateenv_test",
+    srcs = ["feupdateenv_test.cpp"],
+    additional_deps = ["@llvm-project//libc:__support_fputil"],
+    libc_function_deps = ["@llvm-project//libc:feupdateenv"],
+)
+
+libc_test(
+    name = "getenv_and_setenv_test",
+    srcs = ["getenv_and_setenv_test.cpp"],
+    additional_deps = ["@llvm-project//libc:__support_fputil"],
+    libc_function_deps = [
+        "@llvm-project//libc:fegetenv",
+        "@llvm-project//libc:fegetround",
+        "@llvm-project//libc:fesetenv",
+        "@llvm-project//libc:fesetround",
+    ],
+)
diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/math/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/src/math/BUILD.bazel
new file mode 100644
--- /dev/null
+++ b/utils/bazel/llvm-project-overlay/libc/test/src/math/BUILD.bazel
@@ -0,0 +1,457 @@
+# Tests for LLVM libc math.h functions.
+
+load("@llvm-project//libc/test/src/math:libc_math_test_rules.bzl", "math_test")
+
+licenses(["notice"])
+
+math_test(
+    name = "fabs",
+    hdrs = ["FAbsTest.h"],
+)
+
+math_test(
+    name = "fabsf",
+    hdrs = ["FAbsTest.h"],
+)
+
+math_test(
+    name = "fabsl",
+    hdrs = ["FAbsTest.h"],
+)
+
+math_test(
+    name = "ceil",
+    hdrs = ["CeilTest.h"],
+)
+
+math_test(
+    name = "ceilf",
+    hdrs = ["CeilTest.h"],
+)
+
+math_test(
+    name = "ceill",
+    hdrs = ["CeilTest.h"],
+)
+
+math_test(
+    name = "floor",
+    hdrs = ["FloorTest.h"],
+)
+
+math_test(
+    name = "floorf",
+    hdrs = ["FloorTest.h"],
+)
+
+math_test(
+    name = "floorl",
+    hdrs = ["FloorTest.h"],
+)
+
+math_test(
+    name = "trunc",
+    hdrs = ["TruncTest.h"],
+)
+
+math_test(
+    name = "truncf",
+    hdrs = ["TruncTest.h"],
+)
+
+math_test(
+    name = "truncl",
+    hdrs = ["TruncTest.h"],
+)
+
+math_test(
+    name = "round",
+    hdrs = ["RoundTest.h"],
+)
+
+math_test(
+    name = "roundf",
+    hdrs = ["RoundTest.h"],
+)
+
+math_test(
+    name = "roundl",
+    hdrs = ["RoundTest.h"],
+)
+
+math_test(
+    name = "frexp",
+    hdrs = ["FrexpTest.h"],
+)
+
+math_test(
+    name = "frexpf",
+    hdrs = ["FrexpTest.h"],
+)
+
+math_test(
+    name = "frexpl",
+    hdrs = ["FrexpTest.h"],
+)
+
+math_test(
+    name = "hypot",
+    hdrs = ["HypotTest.h"],
+)
+
+math_test(
+    name = "hypotf",
+    hdrs = [
+        "HypotTest.h",
+        "hypotf_hard_to_round.h",
+    ],
+)
+
+math_test(
+    name = "logb",
+    hdrs = ["LogbTest.h"],
+)
+
+math_test(
+    name = "logbf",
+    hdrs = ["LogbTest.h"],
+)
+
+math_test(
+    name = "logbl",
+    hdrs = ["LogbTest.h"],
+)
+
+math_test(
+    name = "modf",
+    hdrs = ["ModfTest.h"],
+)
+
+math_test(
+    name = "modff",
+    hdrs = ["ModfTest.h"],
+)
+
+math_test(
+    name = "modfl",
+    hdrs = ["ModfTest.h"],
+)
+
+cc_library(
+    name = "remquo_test_template",
+    hdrs = ["RemQuoTest.h"],
+    deps = [
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc/utils/MPFRWrapper:mpfr_wrapper",
+        "@llvm-project//libc/utils/UnitTest:LibcUnitTest",
+        "@llvm-project//libc/utils/UnitTest:fp_test_helpers",
+    ],
+)
+
+math_test(
+    name = "remquo",
+    additional_deps = [":remquo_test_template"],
+)
+
+math_test(
+    name = "remquof",
+    additional_deps = [":remquo_test_template"],
+)
+
+math_test(
+    name = "remquol",
+    additional_deps = [":remquo_test_template"],
+)
+
+math_test(
+    name = "fmin",
+    hdrs = ["FMinTest.h"],
+)
+
+math_test(
+    name = "fminf",
+    hdrs = ["FMinTest.h"],
+)
+
+math_test(
+    name = "fminl",
+    hdrs = ["FMinTest.h"],
+)
+
+math_test(
+    name = "fmax",
+    hdrs = ["FMaxTest.h"],
+)
+
+math_test(
+    name = "fmaxf",
+    hdrs = ["FMaxTest.h"],
+)
+
+math_test(
+    name = "fmaxl",
+    hdrs = ["FMaxTest.h"],
+)
+
+math_test(
+    name = "sqrt",
+    hdrs = ["SqrtTest.h"],
+    additional_deps = ["@llvm-project//libc:__support_standalone_cpp"],
+)
+
+math_test(
+    name = "sqrtf",
+    hdrs = ["SqrtTest.h"],
+    additional_deps = ["@llvm-project//libc:__support_standalone_cpp"],
+)
+
+# TODO(sivachandra): sqrtl test currently fails on Aarch64 because of
+# insufficient precision in MPFR leading to https://hal.archives-ouvertes.fr/hal-01091186/document
+# We will comment it out for now and wait for it to get fixed upstream.
+# math_test(name = "sqrtl")
+
+math_test(
+    name = "copysign",
+    hdrs = ["CopySignTest.h"],
+)
+
+math_test(
+    name = "copysignf",
+    hdrs = ["CopySignTest.h"],
+)
+
+math_test(
+    name = "copysignl",
+    hdrs = ["CopySignTest.h"],
+)
+
+cc_library(
+    name = "ilogb_test_template",
+    hdrs = ["ILogbTest.h"],
+    deps = [
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc/utils/UnitTest:LibcUnitTest",
+    ],
+)
+
+math_test(
+    name = "ilogb",
+    additional_deps = [":ilogb_test_template"],
+)
+
+math_test(
+    name = "ilogbf",
+    additional_deps = [":ilogb_test_template"],
+)
+
+math_test(
+    name = "ilogbl",
+    additional_deps = [":ilogb_test_template"],
+)
+
+cc_library(
+    name = "fdim_test_template",
+    hdrs = ["FDimTest.h"],
+    deps = [
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc/utils/UnitTest:LibcUnitTest",
+        "@llvm-project//libc/utils/UnitTest:fp_test_helpers",
+    ],
+)
+
+math_test(
+    name = "fdim",
+    additional_deps = [":fdim_test_template"],
+)
+
+math_test(
+    name = "fdimf",
+    additional_deps = [":fdim_test_template"],
+)
+
+math_test(
+    name = "fdiml",
+    additional_deps = [":fdim_test_template"],
+)
+
+cc_library(
+    name = "ldexp_test_template",
+    hdrs = ["LdExpTest.h"],
+    deps = [
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc/utils/UnitTest:LibcUnitTest",
+        "@llvm-project//libc/utils/UnitTest:fp_test_helpers",
+    ],
+)
+
+math_test(
+    name = "ldexp",
+    additional_deps = [":ldexp_test_template"],
+)
+
+math_test(
+    name = "ldexpf",
+    additional_deps = [":ldexp_test_template"],
+)
+
+math_test(
+    name = "ldexpl",
+    additional_deps = [":ldexp_test_template"],
+)
+
+cc_library(
+    name = "rint_test_template",
+    hdrs = ["RIntTest.h"],
+    deps = [
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc/utils/MPFRWrapper:mpfr_wrapper",
+        "@llvm-project//libc/utils/UnitTest:LibcUnitTest",
+        "@llvm-project//libc/utils/UnitTest:fp_test_helpers",
+    ],
+)
+
+math_test(
+    name = "rint",
+    additional_deps = [":rint_test_template"],
+)
+
+math_test(
+    name = "rintf",
+    additional_deps = [":rint_test_template"],
+)
+
+math_test(
+    name = "rintl",
+    additional_deps = [":rint_test_template"],
+)
+
+cc_library(
+    name = "round_to_integer_test_template",
+    hdrs = ["RoundToIntegerTest.h"],
+    deps = [
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc/utils/MPFRWrapper:mpfr_wrapper",
+        "@llvm-project//libc/utils/UnitTest:LibcUnitTest",
+        "@llvm-project//libc/utils/UnitTest:fp_test_helpers",
+    ],
+)
+
+math_test(
+    name = "lrint",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "lrintf",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "lrintl",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "llrint",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "llrintf",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "llrintl",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "lround",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "lroundf",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "lroundl",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "llround",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "llroundf",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+math_test(
+    name = "llroundl",
+    additional_deps = [":round_to_integer_test_template"],
+)
+
+cc_library(
+    name = "nextafter_test_template",
+    hdrs = ["NextAfterTest.h"],
+    deps = [
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc:__support_standalone_cpp",
+        "@llvm-project//libc/utils/UnitTest:LibcUnitTest",
+        "@llvm-project//libc/utils/UnitTest:fp_test_helpers",
+    ],
+)
+
+math_test(
+    name = "nextafter",
+    additional_deps = [":nextafter_test_template"],
+)
+
+math_test(
+    name = "nextafterf",
+    additional_deps = [":nextafter_test_template"],
+)
+
+math_test(
+    name = "nextafterl",
+    additional_deps = [":nextafter_test_template"],
+)
+
+cc_library(
+    name = "sdcomp26094",
+    hdrs = ["sdcomp26094.h"],
+    deps = [
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc:__support_standalone_cpp",
+        "@llvm-project//libc:libc_root",
+    ],
+)
+
+math_test(
+    name = "cosf",
+    additional_deps = [
+        ":sdcomp26094",
+        "@llvm-project//libc:__support_standalone_cpp",
+    ],
+)
+
+math_test(
+    name = "sincosf",
+    additional_deps = [
+        ":sdcomp26094",
+        "@llvm-project//libc:__support_standalone_cpp",
+    ],
+)
+
+math_test(
+    name = "sinf",
+    additional_deps = [
+        ":sdcomp26094",
+        "@llvm-project//libc:__support_standalone_cpp",
+    ],
+)
diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/math/libc_math_test_rules.bzl b/utils/bazel/llvm-project-overlay/libc/test/src/math/libc_math_test_rules.bzl
new file mode 100644
--- /dev/null
+++ b/utils/bazel/llvm-project-overlay/libc/test/src/math/libc_math_test_rules.bzl
@@ -0,0 +1,30 @@
+load("@llvm-project//libc:test/libc_test_rules.bzl", "libc_test")
+
+def math_test(name, additional_deps = None, need_mpfr = True, hdrs = None):
+    """Add a target for the unittest of a math function.
+
+    Args:
+      name: The name of the function being tested.
+      additional_deps: List of additional depenencies required by the test.
+      need_mpfr: True if the test uses mpfr_wrappper, False otherwise.
+      hdrs: List of headers to add.
+    """
+    test_name = name + "_test"
+    srcs = [test_name + ".cpp"] + (hdrs or [])
+    additional_deps = additional_deps or []
+    libc_function_deps = ["@llvm-project//libc:" + name]
+    additional_deps += [
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc/utils/UnitTest:fp_test_helpers",
+    ]
+    if need_mpfr:
+        additional_deps.append(
+            "@llvm-project//libc/utils/MPFRWrapper:mpfr_wrapper",
+        )
+    libc_test(
+        name = test_name,
+        srcs = srcs,
+        libc_function_deps = libc_function_deps,
+        additional_deps = additional_deps,
+        size = "enormous",  # Some tests are emulated and take very long.
+    )
diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/stdlib/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/src/stdlib/BUILD.bazel
new file mode 100644
--- /dev/null
+++ b/utils/bazel/llvm-project-overlay/libc/test/src/stdlib/BUILD.bazel
@@ -0,0 +1,59 @@
+# Tests for LLVM libc stdlib.h functions.
+
+load("@llvm-project//libc:test/libc_test_rules.bzl", "libc_test")
+
+licenses(["notice"])
+
+libc_test(
+    name = "atoi_test",
+    srcs = ["atoi_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:atoi"],
+)
+
+libc_test(
+    name = "atol_test",
+    srcs = ["atol_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:atol"],
+)
+
+libc_test(
+    name = "atoll_test",
+    srcs = ["atoll_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:atoll"],
+)
+
+libc_test(
+    name = "bsearch_test",
+    srcs = ["bsearch_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:bsearch"],
+)
+
+libc_test(
+    name = "qsort_test",
+    srcs = ["qsort_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:qsort"],
+)
+
+libc_test(
+    name = "strtol_test",
+    srcs = ["strtol_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strtol"],
+)
+
+libc_test(
+    name = "strtoll_test",
+    srcs = ["strtoll_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strtoll"],
+)
+
+libc_test(
+    name = "strtoul_test",
+    srcs = ["strtoul_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strtoul"],
+)
+
+libc_test(
+    name = "strtoull_test",
+    srcs = ["strtoull_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strtoull"],
+)
diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/string/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/src/string/BUILD.bazel
new file mode 100644
--- /dev/null
+++ b/utils/bazel/llvm-project-overlay/libc/test/src/string/BUILD.bazel
@@ -0,0 +1,123 @@
+# Tests for LLVM libc string.h functions.
+
+load("@llvm-project//libc:test/libc_test_rules.bzl", "libc_test")
+
+licenses(["notice"])
+
+libc_test(
+    name = "strlen_test",
+    srcs = ["strlen_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strlen"],
+)
+
+libc_test(
+    name = "strcpy_test",
+    srcs = ["strcpy_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strcpy_sanitized"],
+)
+
+libc_test(
+    name = "strcmp_test",
+    srcs = ["strcmp_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strcmp"],
+)
+
+libc_test(
+    name = "memchr_test",
+    srcs = ["memchr_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:memchr"],
+)
+
+libc_test(
+    name = "strchr_test",
+    srcs = ["strchr_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strchr"],
+)
+
+libc_test(
+    name = "strstr_test",
+    srcs = ["strstr_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strstr"],
+)
+
+libc_test(
+    name = "strnlen_test",
+    srcs = ["strnlen_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strnlen"],
+)
+
+libc_test(
+    name = "memrchr_test",
+    srcs = ["memrchr_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:memrchr"],
+)
+
+libc_test(
+    name = "strrchr_test",
+    srcs = ["strrchr_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strrchr"],
+)
+
+libc_test(
+    name = "strcspn_test",
+    srcs = ["strcspn_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strcspn"],
+)
+
+libc_test(
+    name = "strspn_test",
+    srcs = ["strspn_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strspn"],
+)
+
+libc_test(
+    name = "strtok_test",
+    srcs = ["strtok_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:strtok"],
+)
+
+libc_test(
+    name = "memcpy_test",
+    srcs = ["memcpy_test.cpp"],
+    additional_deps = ["@llvm-project//libc:__support_standalone_cpp"],
+    libc_function_deps = ["@llvm-project//libc:memcpy"],
+)
+
+libc_test(
+    name = "memset_test",
+    srcs = ["memset_test.cpp"],
+    additional_deps = ["@llvm-project//libc:__support_standalone_cpp"],
+    libc_function_deps = ["@llvm-project//libc:memset"],
+)
+
+libc_test(
+    name = "memmove_test",
+    srcs = ["memmove_test.cpp"],
+    additional_deps = [
+        "@llvm-project//libc:__support_standalone_cpp",
+        "@llvm-project//libc/utils/UnitTest:memory_matcher",
+    ],
+    libc_function_deps = [
+        "@llvm-project//libc:memcmp",
+        "@llvm-project//libc:memmove",
+    ],
+)
+
+libc_test(
+    name = "memcmp_test",
+    srcs = ["memcmp_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:memcmp"],
+)
+
+libc_test(
+    name = "bcmp_test",
+    srcs = ["bcmp_test.cpp"],
+    libc_function_deps = ["@llvm-project//libc:bcmp"],
+)
+
+libc_test(
+    name = "bzero_test",
+    srcs = ["bzero_test.cpp"],
+    additional_deps = ["@llvm-project//libc:__support_standalone_cpp"],
+    libc_function_deps = ["@llvm-project//libc:bzero"],
+)
diff --git a/utils/bazel/llvm-project-overlay/libc/utils/MPFRWrapper/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/utils/MPFRWrapper/BUILD.bazel
new file mode 100644
--- /dev/null
+++ b/utils/bazel/llvm-project-overlay/libc/utils/MPFRWrapper/BUILD.bazel
@@ -0,0 +1,19 @@
+# A wrapper library over MPFR for use with LLVM libc math unittests.
+
+licenses(["notice"])
+
+cc_library(
+    name = "mpfr_wrapper",
+    srcs = ["MPFRUtils.cpp"],
+    hdrs = ["MPFRUtils.h"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "@llvm-project//libc:__support_common",
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc:__support_standalone_cpp",
+        "@llvm-project//libc:libc_root",
+        "@llvm-project//libc/utils/UnitTest:LibcUnitTest",
+        "@llvm-project//libc/utils/UnitTest:fp_test_helpers",
+        "@mpfr//:mpfr",
+    ],
+)
diff --git a/utils/bazel/llvm-project-overlay/libc/utils/UnitTest/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/utils/UnitTest/BUILD.bazel
new file mode 100644
--- /dev/null
+++ b/utils/bazel/llvm-project-overlay/libc/utils/UnitTest/BUILD.bazel
@@ -0,0 +1,54 @@
+# LLVM libc unittest library.
+
+licenses(["notice"])
+
+cc_library(
+    name = "LibcUnitTest",
+    srcs = [
+        "LibcTest.cpp",
+        "LibcTestMain.cpp",
+    ],
+    hdrs = [
+        "LibcTest.h",
+        "PlatformDefs.h",
+        "Test.h",
+    ],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//llvm:Support",
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc:__support_standalone_cpp",
+        "@llvm-project//libc:libc_root",
+        "@llvm-project//libc/utils/testutils:libc_test_utils",
+    ],
+)
+
+cc_library(
+    name = "fp_test_helpers",
+    srcs = [
+        "FPExceptMatcher.cpp",
+        "FPMatcher.cpp",
+    ],
+    hdrs = [
+        "FPExceptMatcher.h",
+        "FPMatcher.h",
+    ],
+    visibility = ["//visibility:public"],
+    deps = [
+        ":LibcUnitTest",
+        "@llvm-project//libc:__support_fputil",
+        "@llvm-project//libc:__support_standalone_cpp",
+        "@llvm-project//libc:libc_root",
+    ],
+)
+
+cc_library(
+    name = "memory_matcher",
+    srcs = ["MemoryMatcher.cpp"],
+    hdrs = ["MemoryMatcher.h"],
+    visibility = ["//visibility:public"],
+    deps = [
+        ":LibcUnitTest",
+        "@llvm-project//libc:__support_standalone_cpp",
+    ],
+)
diff --git a/utils/bazel/llvm-project-overlay/libc/utils/testutils/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/utils/testutils/BUILD.bazel
new file mode 100644
--- /dev/null
+++ b/utils/bazel/llvm-project-overlay/libc/utils/testutils/BUILD.bazel
@@ -0,0 +1,20 @@
+licenses(["notice"])
+
+cc_library(
+    name = "libc_test_utils",
+    srcs = [
+        "ExecuteFunctionUnix.cpp",
+        "FDReaderUnix.cpp",
+        "StreamWrapper.cpp",
+    ],
+    hdrs = [
+        "ExecuteFunction.h",
+        "FDReader.h",
+        "StreamWrapper.h",
+    ],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//llvm:Support",
+        "@llvm-project//libc:libc_root",
+    ],
+)
diff --git a/utils/bazel/third_party_build/gmp.BUILD b/utils/bazel/third_party_build/gmp.BUILD
new file mode 100644
--- /dev/null
+++ b/utils/bazel/third_party_build/gmp.BUILD
@@ -0,0 +1,14 @@
+load("@rules_foreign_cc//foreign_cc:defs.bzl", "configure_make")
+
+filegroup(
+    name = "sources",
+    srcs = glob(["**"]),
+)
+
+configure_make(
+    name = "gmp",
+    copts = ["-Wno-error"],  # ./configure crashes with `-Werror`
+    lib_name = "libgmp",
+    lib_source = ":sources",
+    visibility = ["//visibility:public"],
+)
diff --git a/utils/bazel/third_party_build/mpfr.BUILD b/utils/bazel/third_party_build/mpfr.BUILD
new file mode 100644
--- /dev/null
+++ b/utils/bazel/third_party_build/mpfr.BUILD
@@ -0,0 +1,15 @@
+load("@rules_foreign_cc//foreign_cc:defs.bzl", "configure_make")
+
+filegroup(
+    name = "sources",
+    srcs = glob(["**"]),
+)
+
+configure_make(
+    name = "mpfr",
+    copts = ["-Wno-error"],  # ./configure crashes with `-Werror`
+    lib_name = "libmpfr",
+    lib_source = ":sources",
+    visibility = ["//visibility:public"],
+    deps = ["@gmp"],
+)