diff --git a/compiler-rt/CMakeLists.txt b/compiler-rt/CMakeLists.txt
--- a/compiler-rt/CMakeLists.txt
+++ b/compiler-rt/CMakeLists.txt
@@ -500,11 +500,11 @@
 # move some of the common flags to COMPILER_RT_UNITTEST_CFLAGS.
 
 # Unittests need access to C++ standard library.
-string(APPEND COMPILER_RT_TEST_COMPILER_CFLAGS " ${stdlib_flag}")
+string(APPEND COMPILER_RT_TOOLCHAIN_CFLAGS " ${stdlib_flag}")
 
-# When cross-compiling, COMPILER_RT_TEST_COMPILER_CFLAGS help in compilation
-# and linking of unittests.
-string(REPLACE " " ";" COMPILER_RT_UNITTEST_CFLAGS "${COMPILER_RT_TEST_COMPILER_CFLAGS}")
+# When cross-compiling or using a non-default toolchain,
+# COMPILER_RT_TOOLCHAIN_CFLAGS help in compilation and linking of unittests.
+string(REPLACE " " ";" COMPILER_RT_UNITTEST_CFLAGS "${COMPILER_RT_TOOLCHAIN_CFLAGS}")
 set(COMPILER_RT_UNITTEST_LINK_FLAGS ${COMPILER_RT_UNITTEST_CFLAGS})
 
 # Unittests support.
diff --git a/compiler-rt/cmake/Modules/AddCompilerRT.cmake b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
--- a/compiler-rt/cmake/Modules/AddCompilerRT.cmake
+++ b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
@@ -570,6 +570,8 @@
   set(PASSTHROUGH_VARIABLES
     CMAKE_C_COMPILER_TARGET
     CMAKE_CXX_COMPILER_TARGET
+    CMAKE_C_COMPILER_EXTERNAL_TOOLCHAIN
+    CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN
     CMAKE_SHARED_LINKER_FLAGS
     CMAKE_MODULE_LINKER_FLAGS
     CMAKE_EXE_LINKER_FLAGS
diff --git a/compiler-rt/cmake/base-config-ix.cmake b/compiler-rt/cmake/base-config-ix.cmake
--- a/compiler-rt/cmake/base-config-ix.cmake
+++ b/compiler-rt/cmake/base-config-ix.cmake
@@ -227,4 +227,12 @@
     endif()
     set(COMPILER_RT_OS_SUFFIX "")
   endif()
+  # Set up options associated with the toolchain.
+  if(COMPILER_RT_TEST_COMPILER_CFLAGS)
+    # COMPILER_RT_TEST_COMPILER_CFLAGS is used for cross-compiling.
+    set(COMPILER_RT_TOOLCHAIN_CFLAGS ${COMPILER_RT_TEST_COMPILER_CFLAGS})
+  elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN AND COMPILER_RT_TEST_COMPILER_ID MATCHES "Clang")
+    # Use the non-default toolchain specified for the build when compiling tests.
+    set(COMPILER_RT_TOOLCHAIN_CFLAGS "--gcc-toolchain=${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
+  endif()
 endmacro()
diff --git a/compiler-rt/cmake/config-ix.cmake b/compiler-rt/cmake/config-ix.cmake
--- a/compiler-rt/cmake/config-ix.cmake
+++ b/compiler-rt/cmake/config-ix.cmake
@@ -229,6 +229,7 @@
     if(APPLE)
       list(APPEND ${cflags_out} ${DARWIN_osx_CFLAGS})
     endif()
+    list(APPEND ${cflags_out} ${COMPILER_RT_TOOLCHAIN_CFLAGS})
     string(REPLACE ";" " " ${cflags_out} "${${cflags_out}}")
   endif()
 endmacro()
@@ -244,7 +245,7 @@
   get_target_flags_for_arch(${arch} test_cflags)
   list(APPEND test_cflags ${DARWIN_${platform}_CFLAGS})
   string(REPLACE ";" " " test_cflags_str "${test_cflags}")
-  string(APPEND test_cflags_str "${COMPILER_RT_TEST_COMPILER_CFLAGS}")
+  string(APPEND test_cflags_str "${COMPILER_RT_TOOLCHAIN_CFLAGS}")
   set(${cflags_out} "${test_cflags_str}" PARENT_SCOPE)
 endfunction()
 
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
@@ -7,7 +7,7 @@
 
 # Generic config options for all compiler-rt lit tests.
 set_default("target_triple", "@COMPILER_RT_DEFAULT_TARGET_TRIPLE@")
-set_default("target_cflags", "@COMPILER_RT_TEST_COMPILER_CFLAGS@")
+set_default("target_cflags", "@COMPILER_RT_TOOLCHAIN_CFLAGS@")
 set_default("host_arch", "@HOST_ARCH@")
 set_default("target_arch", "@COMPILER_RT_DEFAULT_TARGET_ARCH@")
 set_default("host_os", "@HOST_OS@")