diff --git a/libcxx/test/configs/cmake-bridge.cfg.in b/libcxx/test/configs/cmake-bridge.cfg.in
--- a/libcxx/test/configs/cmake-bridge.cfg.in
+++ b/libcxx/test/configs/cmake-bridge.cfg.in
@@ -2,6 +2,8 @@
 
 @SERIALIZED_LIT_PARAMS@
 
+import lit
+
 #
 # This file performs the bridge between the CMake configuration and the Lit
 # configuration files by setting up the LitConfig object and various Lit
@@ -23,7 +25,7 @@
 config.test_exec_root = '@CMAKE_BINARY_DIR@'
 
 # Add substitutions for bootstrapping the test suite configuration
-config.substitutions.append(('%{cxx}', '@CMAKE_CXX_COMPILER@'))
+config.substitutions.append(('%{cxx}', lit.TestRunner.quote('@CMAKE_CXX_COMPILER@')))
 config.substitutions.append(('%{libcxx}', '@LIBCXX_SOURCE_DIR@'))
 config.substitutions.append(('%{install}', '@CMAKE_BINARY_DIR@'))
 config.substitutions.append(('%{include}', '%{install}/@LIBCXX_INSTALL_INCLUDE_DIR@'))
diff --git a/libcxx/test/configs/llvm-libc++-mingw.cfg.in b/libcxx/test/configs/llvm-libc++-mingw.cfg.in
new file mode 100644
--- /dev/null
+++ b/libcxx/test/configs/llvm-libc++-mingw.cfg.in
@@ -0,0 +1,32 @@
+# This testing configuration handles running the test suite against LLVM's libc++
+# using either a DLL or a static library, with MinGW/Clang on Windows.
+
+lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
+
+config.substitutions.append(('%{flags}', ''))
+config.substitutions.append(('%{compile_flags}',
+    '%{user_compile_flags} -nostdinc++ -isystem %{include} -isystem %{target-include} -I %{libcxx}/test/support'
+))
+config.substitutions.append(('%{link_flags}',
+    '%{user_link_flags} -nostdlib++ -L %{lib} -lc++'
+))
+config.substitutions.append(('%{exec}',
+    '%{executor} --execdir %T --env PATH=%{lib} -- '
+))
+
+# LIBCXX-WINDOWS-FIXME is the feature name used to XFAIL the
+# initial Windows failures until they can be properly diagnosed
+# and fixed. This allows easier detection of new test failures
+# and regressions. Note: New failures should not be suppressed
+# using this feature. (Also see llvm.org/PR32730)
+config.available_features.add('LIBCXX-WINDOWS-FIXME')
+
+import os, site
+site.addsitedir(os.path.join('@LIBCXX_SOURCE_DIR@', 'utils'))
+import libcxx.test.params, libcxx.test.newconfig
+libcxx.test.newconfig.configure(
+    libcxx.test.params.DEFAULT_PARAMETERS,
+    libcxx.test.features.DEFAULT_FEATURES,
+    config,
+    lit_config
+)
diff --git a/libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in b/libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in
new file mode 100644
--- /dev/null
+++ b/libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in
@@ -0,0 +1,32 @@
+# This testing configuration handles running the test suite against LLVM's libc++
+# using a DLL, with Clang-cl on Windows.
+
+lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
+
+config.substitutions.append(('%{flags}', '--driver-mode=g++'))
+config.substitutions.append(('%{compile_flags}',
+    '%{user_compile_flags} -nostdinc++ -isystem %{include} -isystem %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX'
+))
+config.substitutions.append(('%{link_flags}',
+    '%{user_link_flags} -nostdlib -L %{lib} -lc++ -lmsvcrt -lmsvcprt -loldnames'
+))
+config.substitutions.append(('%{exec}',
+    '%{executor} --execdir %T --env PATH=%{lib} -- '
+))
+
+# LIBCXX-WINDOWS-FIXME is the feature name used to XFAIL the
+# initial Windows failures until they can be properly diagnosed
+# and fixed. This allows easier detection of new test failures
+# and regressions. Note: New failures should not be suppressed
+# using this feature. (Also see llvm.org/PR32730)
+config.available_features.add('LIBCXX-WINDOWS-FIXME')
+
+import os, site
+site.addsitedir(os.path.join('@LIBCXX_SOURCE_DIR@', 'utils'))
+import libcxx.test.params, libcxx.test.newconfig
+libcxx.test.newconfig.configure(
+    libcxx.test.params.DEFAULT_PARAMETERS,
+    libcxx.test.features.DEFAULT_FEATURES,
+    config,
+    lit_config
+)
diff --git a/libcxx/test/configs/llvm-libc++-static-clangcl.cfg.in b/libcxx/test/configs/llvm-libc++-static-clangcl.cfg.in
new file mode 100644
--- /dev/null
+++ b/libcxx/test/configs/llvm-libc++-static-clangcl.cfg.in
@@ -0,0 +1,32 @@
+# This testing configuration handles running the test suite against LLVM's libc++
+# using a static library, with Clang-cl on Windows.
+
+lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
+
+config.substitutions.append(('%{flags}', '--driver-mode=g++'))
+config.substitutions.append(('%{compile_flags}',
+    '%{user_compile_flags} -nostdinc++ -isystem %{include} -isystem %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX'
+))
+config.substitutions.append(('%{link_flags}',
+    '%{user_link_flags} -nostdlib -L %{lib} -llibc++ -lmsvcrt -lmsvcprt -loldnames'
+))
+config.substitutions.append(('%{exec}',
+    '%{executor} --execdir %T --env PATH=%{lib} -- '
+))
+
+# LIBCXX-WINDOWS-FIXME is the feature name used to XFAIL the
+# initial Windows failures until they can be properly diagnosed
+# and fixed. This allows easier detection of new test failures
+# and regressions. Note: New failures should not be suppressed
+# using this feature. (Also see llvm.org/PR32730)
+config.available_features.add('LIBCXX-WINDOWS-FIXME')
+
+import os, site
+site.addsitedir(os.path.join('@LIBCXX_SOURCE_DIR@', 'utils'))
+import libcxx.test.params, libcxx.test.newconfig
+libcxx.test.newconfig.configure(
+    libcxx.test.params.DEFAULT_PARAMETERS,
+    libcxx.test.features.DEFAULT_FEATURES,
+    config,
+    lit_config
+)
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -598,13 +598,15 @@
     # correctly when libc++ visibility attributes indicate dllimport linkage
     # anyway), thus just disable the experimental library. Remove this
     # setting when cmake and the test driver does the right thing automatically.
-    generate-cmake-libcxx-win -DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=OFF
+    generate-cmake-libcxx-win -DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=OFF \
+                              -DLIBCXX_TEST_CONFIG="llvm-libc++-shared-clangcl.cfg.in"
     echo "+++ Running the libc++ tests"
     ${NINJA} -vC "${BUILD_DIR}" check-cxx
 ;;
 clang-cl-static)
     clean
-    generate-cmake-libcxx-win -DLIBCXX_ENABLE_SHARED=OFF
+    generate-cmake-libcxx-win -DLIBCXX_ENABLE_SHARED=OFF \
+                              -DLIBCXX_TEST_CONFIG="llvm-libc++-static-clangcl.cfg.in"
     echo "+++ Running the libc++ tests"
     ${NINJA} -vC "${BUILD_DIR}" check-cxx
 ;;
@@ -618,6 +620,7 @@
     generate-cmake \
           -DCMAKE_C_COMPILER=x86_64-w64-mingw32-clang \
           -DCMAKE_CXX_COMPILER=x86_64-w64-mingw32-clang++ \
+          -DLIBCXX_TEST_CONFIG="llvm-libc++-mingw.cfg.in" \
           -C "${MONOREPO_ROOT}/libcxx/cmake/caches/MinGW.cmake"
     echo "+++ Running the libc++ tests"
     ${NINJA} -vC "${BUILD_DIR}" check-cxx
@@ -627,6 +630,7 @@
     generate-cmake \
           -DCMAKE_C_COMPILER=x86_64-w64-mingw32-clang \
           -DCMAKE_CXX_COMPILER=x86_64-w64-mingw32-clang++ \
+          -DLIBCXX_TEST_CONFIG="llvm-libc++-mingw.cfg.in" \
           -C "${MONOREPO_ROOT}/libcxx/cmake/caches/MinGW.cmake" \
           -DLIBCXX_ENABLE_SHARED=OFF \
           -DLIBUNWIND_ENABLE_SHARED=OFF
diff --git a/libcxx/utils/libcxx/test/format.py b/libcxx/utils/libcxx/test/format.py
--- a/libcxx/utils/libcxx/test/format.py
+++ b/libcxx/utils/libcxx/test/format.py
@@ -21,7 +21,7 @@
     This is done by checking whether the %{cxx} substitution in that
     configuration supports certain compiler flags.
     """
-    command = "%{{cxx}} -xc++ {} -Werror -fsyntax-only -Xclang -verify-ignore-unexpected".format(os.devnull)
+    command = "%{{cxx}} %{{flags}} %{{compile_flags}} -xc++ {} -Werror -fsyntax-only -Xclang -verify-ignore-unexpected".format(os.devnull)
     command = lit.TestRunner.applySubstitutions([command], config.substitutions,
                                                 recursion_limit=config.recursiveExpansionLimit)[0]
     devNull = open(os.devnull, 'w')
diff --git a/llvm/utils/lit/lit/LitConfig.py b/llvm/utils/lit/lit/LitConfig.py
--- a/llvm/utils/lit/lit/LitConfig.py
+++ b/llvm/utils/lit/lit/LitConfig.py
@@ -169,6 +169,11 @@
         line = inspect.getlineno(f)
         sys.stderr.write('%s: %s:%d: %s: %s\n' % (self.progname, file, line,
                                                   kind, message))
+        if self.isWindows:
+            # In an msys terminal, the writes to sys.stderr aren't visible
+            # on screen immediately. Flush them here to avoid broken/misoredered
+            # output.
+            sys.stderr.flush()
 
     def note(self, message):
         if not self.quiet:
diff --git a/llvm/utils/lit/lit/TestRunner.py b/llvm/utils/lit/lit/TestRunner.py
--- a/llvm/utils/lit/lit/TestRunner.py
+++ b/llvm/utils/lit/lit/TestRunner.py
@@ -7,6 +7,7 @@
 import re
 import stat
 import platform
+import shlex
 import shutil
 import tempfile
 import threading
@@ -239,6 +240,11 @@
 
     return ''.join(result)
 
+def quote(arg):
+    if kIsWindows:
+        return quote_windows_command([arg])
+    return shlex.quote(arg)
+
 # args are from 'export' or 'env' command.
 # Skips the command, and parses its arguments.
 # Modifies env accordingly.