diff --git a/clang/cmake/caches/Fuchsia-stage2.cmake b/clang/cmake/caches/Fuchsia-stage2.cmake
--- a/clang/cmake/caches/Fuchsia-stage2.cmake
+++ b/clang/cmake/caches/Fuchsia-stage2.cmake
@@ -69,12 +69,44 @@
   set(RUNTIMES_CMAKE_ARGS "-DCMAKE_OSX_DEPLOYMENT_TARGET=10.13;-DCMAKE_OSX_ARCHITECTURES=arm64|x86_64" CACHE STRING "")
 endif()
 
-if(WIN32)
+if(WIN32 OR LLVM_WINSYSROOT)
+  if((NOT WIN32) AND (NOT LLVM_VFSOVERLAY))
+    message(FATAL_ERROR "LLVM_VFSOVERLAY should be defined.")
+  endif()
   set(target "x86_64-pc-windows-msvc")
 
+  if (LLVM_WINSYSROOT)
+    set(WINDOWS_COMPILER_FLAGS
+      -Xclang
+      -ivfsoverlay
+      -Xclang
+      ${LLVM_VFSOVERLAY}
+      # TODO: /winsysroot should be set by HandleLLVMOptions.cmake automatically
+      # but it current has a bug that prevents it from working under cross
+      # compilation. Set this flag manually for now.
+      /winsysroot
+      ${LLVM_WINSYSROOT})
+    string(REPLACE ";" " " WINDOWS_COMPILER_FLAGS "${WINDOWS_COMPILER_FLAGS}")
+    set(WINDOWS_LINK_FLAGS
+        /vfsoverlay:${LLVM_VFSOVERLAY}
+        # TODO: On Windows, linker is invoked by cmake instead of the clang-cl driver,
+        # so we have to manually set the libpath. We use clang-cl driver if we can
+        # and remove these libpath flags.
+        -libpath:"${LLVM_WINSYSROOT}/VC/Tools/MSVC/14.34.31933/lib/x64"
+        -libpath:"${LLVM_WINSYSROOT}/VC/Tools/MSVC/14.34.31933/atlmfc/lib/x64"
+        -libpath:"${LLVM_WINSYSROOT}/Windows Kits/10/Lib/10.0.19041.0/ucrt/x64"
+        -libpath:"${LLVM_WINSYSROOT}/Windows Kits/10/Lib/10.0.19041.0/um/x64")
+    string(REPLACE ";" " " WINDOWS_LINK_FLAGS "${WINDOWS_LINK_FLAGS}")
+  endif()
+
   list(APPEND BUILTIN_TARGETS "${target}")
   set(BUILTINS_${target}_CMAKE_SYSTEM_NAME Windows CACHE STRING "")
   set(BUILTINS_${target}_CMAKE_BUILD_TYPE RelWithDebInfo CACHE STRING "")
+  set(BUILTINS_${target}_CMAKE_C_FLAGS ${WINDOWS_COMPILER_FLAGS} CACHE STRING "")
+  set(BUILTINS_${target}_CMAKE_CXX_FLAGS ${WINDOWS_COMPILER_FLAGS} CACHE STRING "")
+  set(BUILTINS_${target}_CMAKE_EXE_LINKER_FLAGS ${WINDOWS_LINK_FLAGS} CACHE STRING "")
+  set(BUILTINS_${target}_CMAKE_SHARED_LINKER_FLAGS ${WINDOWS_LINK_FLAGS} CACHE STRING "")
+  set(BUILTINS_${target}_CMAKE_MODULE_LINKER_FLAGS ${WINDOWS_LINK_FLAGS} CACHE STRING "")
 
   list(APPEND RUNTIME_TARGETS "${target}")
   set(RUNTIMES_${target}_CMAKE_SYSTEM_NAME Windows CACHE STRING "")
@@ -84,6 +116,11 @@
   set(RUNTIMES_${target}_LIBCXX_ENABLE_ABI_LINKER_SCRIPT OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx" CACHE STRING "")
+  set(RUNTIMES_${target}_CMAKE_C_FLAGS ${WINDOWS_COMPILER_FLAGS} CACHE STRING "")
+  set(RUNTIMES_${target}_CMAKE_CXX_FLAGS ${WINDOWS_COMPILER_FLAGS} CACHE STRING "")
+  set(RUNTIMES_${target}_CMAKE_EXE_LINKER_FLAGS ${WINDOWS_LINK_FLAGS} CACHE STRING "")
+  set(RUNTIMES_${target}_CMAKE_SHARED_LINKER_FLAGS ${WINDOWS_LINK_FLAGS} CACHE STRING "")
+  set(RUNTIMES_${target}_CMAKE_MODULE_LINKER_FLAGS ${WINDOWS_LINK_FLAGS} CACHE STRING "")
 endif()
 
 foreach(target aarch64-unknown-linux-gnu;armv7-unknown-linux-gnueabihf;i386-unknown-linux-gnu;x86_64-unknown-linux-gnu)
diff --git a/llvm/cmake/modules/LLVMExternalProjectUtils.cmake b/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
--- a/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
+++ b/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
@@ -93,7 +93,7 @@
       if(_cmake_system_name STREQUAL Darwin)
         list(APPEND ARG_TOOLCHAIN_TOOLS llvm-libtool-darwin llvm-lipo)
       elseif(is_msvc_target)
-        list(APPEND ARG_TOOLCHAIN_TOOLS llvm-lib)
+        list(APPEND ARG_TOOLCHAIN_TOOLS llvm-lib llvm-rc llvm-mt)
       else()
         # TODO: These tools don't fully support Mach-O format yet.
         list(APPEND ARG_TOOLCHAIN_TOOLS llvm-objcopy llvm-strip llvm-readelf)
@@ -213,6 +213,12 @@
     if(llvm-readelf IN_LIST TOOLCHAIN_TOOLS)
       list(APPEND compiler_args -DCMAKE_READELF=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-readelf${CMAKE_EXECUTABLE_SUFFIX})
     endif()
+    if(llvm-mt IN_LIST TOOLCHAIN_TOOLS AND is_msvc_target)
+      list(APPEND compiler_args -DCMAKE_MT=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-mt${CMAKE_EXECUTABLE_SUFFIX})
+    endif()
+    if(llvm-rc IN_LIST TOOLCHAIN_TOOLS AND is_msvc_target)
+      list(APPEND compiler_args -DCMAKE_RC_COMPILER=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-rc${CMAKE_EXECUTABLE_SUFFIX})
+    endif()
     list(APPEND ARG_DEPENDS ${TOOLCHAIN_TOOLS})
   endif()