diff --git a/compiler-rt/test/CMakeLists.txt b/compiler-rt/test/CMakeLists.txt
--- a/compiler-rt/test/CMakeLists.txt
+++ b/compiler-rt/test/CMakeLists.txt
@@ -1,6 +1,16 @@
 # Needed for lit support in standalone builds.
 include(AddLLVM)
 
+option(COMPILER_RT_TEST_STANDALONE_BUILD_LIBS
+  "When set to ON and testing in a standalone build, test the runtime \
+  libraries built by this standalone build rather than the runtime libraries \
+  shipped with the compiler (used for testing). When set to OFF and testing \
+  in a standalone build, test the runtime libraries shipped with the compiler \
+  (used for testing). This option has no effect if the compiler and this \
+  build are configured to use the same runtime library path."
+  ON)
+pythonize_bool(COMPILER_RT_TEST_STANDALONE_BUILD_LIBS)
+
 pythonize_bool(LLVM_ENABLE_EXPENSIVE_CHECKS)
 configure_compiler_rt_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.common.configured.in
diff --git a/compiler-rt/test/builtins/Unit/lit.site.cfg.py.in b/compiler-rt/test/builtins/Unit/lit.site.cfg.py.in
--- a/compiler-rt/test/builtins/Unit/lit.site.cfg.py.in
+++ b/compiler-rt/test/builtins/Unit/lit.site.cfg.py.in
@@ -7,6 +7,7 @@
 config.is_msvc = @MSVC_PYBOOL@
 config.builtins_is_msvc = @BUILTINS_IS_MSVC_PYBOOL@
 config.builtins_lit_source_features = "@BUILTINS_LIT_SOURCE_FEATURES@"
+config.test_suite_supports_overriding_runtime_lib_path = True
 
 # Load common config for all compiler-rt lit tests.
 lit_config.load_config(config, "@COMPILER_RT_BINARY_DIR@/test/lit.common.configured")
diff --git a/compiler-rt/test/lit.common.cfg.py b/compiler-rt/test/lit.common.cfg.py
--- a/compiler-rt/test/lit.common.cfg.py
+++ b/compiler-rt/test/lit.common.cfg.py
@@ -21,6 +21,60 @@
   import pipes
   sh_quote = pipes.quote
 
+def find_compiler_libdir():
+  """
+    Returns the path to library resource directory used
+    by the compiler.
+  """
+  if config.compiler_id != 'Clang':
+    lit_config.warning(f'Determining compiler\'s runtime directory is not supported for {config.compiler_id}')
+    # TODO: Support other compilers.
+    return None
+  def get_path_from_clang(args, allow_failure):
+    clang_cmd = [
+      config.clang.strip(),
+      f'--target={config.target_triple}',
+    ]
+    clang_cmd.extend(args)
+    path = None
+    try:
+      result = subprocess.run(
+        clang_cmd,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        check=True
+      )
+      path = result.stdout.decode().strip()
+    except subprocess.CalledProcessError as e:
+      msg = f'Failed to run {clang_cmd}\nrc:{e.returncode}\nstdout:{e.stdout}\ne.stderr{e.stderr}'
+      if allow_failure:
+        lit_config.warning(msg)
+      else:
+        lit_config.fatal(msg)
+    return path
+
+  # Try using `-print-runtime-dir`. This is only supported by very new versions of Clang.
+  # so allow failure here.
+  runtime_dir = get_path_from_clang(['-print-runtime-dir'], allow_failure=True)
+  if runtime_dir:
+    if os.path.exists(runtime_dir):
+      return os.path.realpath(runtime_dir)
+    lit_config.fatal(f'Path reported by clang does not exist: {runtime_dir}')
+
+  # Fall back for older AppleClang that doesn't support `-print-runtime-dir`
+  # Note `-print-file-name=<path to compiler-rt lib>` was broken for Apple
+  # platforms so we can't use that approach here (see https://reviews.llvm.org/D101682).
+  if config.host_os == 'Darwin':
+    lib_dir = get_path_from_clang(['-print-file-name=lib'], allow_failure=False)
+    runtime_dir = os.path.join(lib_dir, 'darwin')
+    if not os.path.exists(runtime_dir):
+      lit_config.fatal(f'Path reported by clang does not exist: {runtime_dir}')
+    return os.path.realpath(runtime_dir)
+
+  lit_config.warning('Failed to determine compiler\'s runtime directory')
+  return None
+
+
 # Choose between lit's internal shell pipeline runner and a real shell.  If
 # LIT_USE_INTERNAL_SHELL is in the environment, we use that as an override.
 use_lit_shell = os.environ.get("LIT_USE_INTERNAL_SHELL")
@@ -63,6 +117,35 @@
 # Add compiler ID to the list of available features.
 config.available_features.add(compiler_id)
 
+# Ask the compiler for the path to libraries it is going to use. If this
+# doesn't match config.compiler_rt_libdir then it means we might be testing the
+# compiler's own runtime libraries rather than the ones we just built.
+# Warn about about this and handle appropriately.
+compiler_libdir = find_compiler_libdir()
+if compiler_libdir:
+  compiler_rt_libdir_real = os.path.realpath(config.compiler_rt_libdir)
+  if compiler_libdir != compiler_rt_libdir_real:
+    lit_config.warning(
+      'Compiler lib dir != compiler-rt lib dir\n'
+      f'Compiler libdir:     "{compiler_libdir}"\n'
+      f'compiler-rt libdir:  "{compiler_rt_libdir_real}"')
+    if config.test_standalone_build_libs:
+      # Use just built runtime libraries, i.e. the the libraries this built just built.
+      if not config.test_suite_supports_overriding_runtime_lib_path:
+        # Test suite doesn't support this configuration.
+        lit_config.fatal(
+            'COMPILER_RT_TEST_STANDALONE_BUILD_LIBS=ON, but this test suite '
+            'does not support testing the just-built runtime libraries '
+            'when the test compiler is configured to use different runtime '
+            'libraries. Either modify this test suite to support this test '
+            'configuration, or set COMPILER_RT_TEST_STANDALONE_BUILD_LIBS=OFF '
+            'to test the runtime libraries included in the compiler instead.'
+        )
+    else:
+      # Use Compiler's resource library directory instead.
+      config.compiler_rt_libdir = compiler_libdir
+    lit_config.note(f'Testing using libraries in "{config.compiler_rt_libdir}"')
+
 # If needed, add cflag for shadow scale.
 if config.asan_shadow_scale != '':
   config.target_cflags += " -mllvm -asan-mapping-scale=" + config.asan_shadow_scale
diff --git a/compiler-rt/test/lit.common.configured.in b/compiler-rt/test/lit.common.configured.in
--- a/compiler-rt/test/lit.common.configured.in
+++ b/compiler-rt/test/lit.common.configured.in
@@ -46,6 +46,11 @@
 set_default("have_rpc_xdr_h", @HAVE_RPC_XDR_H@)
 set_default("gwp_asan", @COMPILER_RT_HAS_GWP_ASAN_PYBOOL@)
 set_default("expensive_checks", @LLVM_ENABLE_EXPENSIVE_CHECKS_PYBOOL@)
+set_default("test_standalone_build_libs", @COMPILER_RT_TEST_STANDALONE_BUILD_LIBS_PYBOOL@)
+# True iff the test suite supports ignoring the test compiler's runtime library path
+# and using `config.compiler_rt_libdir` instead. This only matters when the runtime
+# library paths differ.
+set_default("test_suite_supports_overriding_runtime_lib_path", False)
 config.available_features.add('target-is-%s' % config.target_arch)
 
 if config.enable_per_target_runtime_dir: