diff --git a/compiler-rt/cmake/Modules/CompilerRTMockLLVMCMakeConfig.cmake b/compiler-rt/cmake/Modules/CompilerRTMockLLVMCMakeConfig.cmake
--- a/compiler-rt/cmake/Modules/CompilerRTMockLLVMCMakeConfig.cmake
+++ b/compiler-rt/cmake/Modules/CompilerRTMockLLVMCMakeConfig.cmake
@@ -46,8 +46,14 @@
     if ("${CMAKE_C_COMPILER_ID}" MATCHES "Clang|GNU")
       # Note: Clang also supports `-print-target-triple` but gcc doesn't
       # support this flag.
+      set(DUMPMACHINE_ARG -dumpmachine)
+      if(MSVC)
+        # This means we are using clang-cl and it requires
+        # /clang: as prefix for dumpmachine argument.
+        set(DUMPMACHINE_ARG /clang:-dumpmachine)
+      endif()
       execute_process(
-        COMMAND "${CMAKE_C_COMPILER}" -dumpmachine
+        COMMAND "${CMAKE_C_COMPILER}" ${DUMPMACHINE_ARG}
         RESULT_VARIABLE HAD_ERROR
         OUTPUT_VARIABLE COMPILER_OUTPUT
         OUTPUT_STRIP_TRAILING_WHITESPACE)