diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -556,6 +556,7 @@
   message(STATUS "Setting current clang stage to: ${CLANG_STAGE}")
 endif()
 
+message(NOTICE "CLANG_ENABLE_BOOTSTRAP is ${CLANG_ENABLE_BOOTSTRAP}")
 if (CLANG_ENABLE_BOOTSTRAP)
   include(ExternalProject)
 
@@ -595,13 +596,14 @@
     add_dependencies(clang-bootstrap-deps lld)
   endif()
 
-  if (WIN32)
+  # message(NOTICE "CMAKE_CROSSCOMPILING is ${CMAKE_CROSSCOMPILING}")
+  # if (WIN32 OR CMAKE_CROSSCOMPILING)
     # Build llvm-rc and llvm-mt which are needed by the Windows build.
-    add_dependencies(clang-bootstrap-deps llvm-rc)
-    if(LLVM_ENABLE_LIBXML2)
-      add_dependencies(clang-bootstrap-deps llvm-mt)
-    endif()
+  add_dependencies(clang-bootstrap-deps llvm-rc llvm-lib)
+  if(LLVM_ENABLE_LIBXML2)
+    add_dependencies(clang-bootstrap-deps llvm-mt)
   endif()
+  # endif()
 
   # If the next stage is LTO we need to depend on LTO and possibly lld or LLVMgold
   if(BOOTSTRAP_LLVM_ENABLE_LTO OR LLVM_ENABLE_LTO AND NOT LLVM_BUILD_INSTRUMENTED)
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
@@ -165,6 +165,9 @@
     endforeach()
   endforeach()
 
+  message(NOTICE "extproj ARG_USE_TOOLCHAIN is ${ARG_USE_TOOLCHAIN}")
+  message(NOTICE "extproj CMAKE_CROSSCOMPILING is ${CMAKE_CROSSCOMPILING}")
+  message(NOTICE "extproj CLANG_IN_TOOLCHAIN is ${CLANG_IN_TOOLCHAIN}")
   if(ARG_USE_TOOLCHAIN AND NOT CMAKE_CROSSCOMPILING)
     if(CLANG_IN_TOOLCHAIN)
       if(is_msvc_target)
@@ -249,18 +252,40 @@
   endif()
 
   if(CMAKE_CROSSCOMPILING OR _cmake_system_name STREQUAL AIX)
-    set(compiler_args -DCMAKE_ASM_COMPILER=${CMAKE_ASM_COMPILER}
-                      -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
-                      -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
-                      -DCMAKE_LINKER=${CMAKE_LINKER}
-                      -DCMAKE_AR=${CMAKE_AR}
-                      -DCMAKE_RANLIB=${CMAKE_RANLIB}
-                      -DCMAKE_NM=${CMAKE_NM}
-                      -DCMAKE_OBJCOPY=${CMAKE_OBJCOPY}
-                      -DCMAKE_OBJDUMP=${CMAKE_OBJDUMP}
-                      -DCMAKE_STRIP=${CMAKE_STRIP}
-                      -DCMAKE_READELF=${CMAKE_READELF})
+    if (ARG_USE_TOOLCHAIN AND CLANG_IN_TOOLCHAIN AND is_msvc_target)
+      get_filename_component(HOST_TOOLCHAIN_DIR ${CMAKE_C_COMPILER} DIRECTORY)
+      set(compiler_args -DCMAKE_C_COMPILER=${HOST_TOOLCHAIN_DIR}/clang-cl${CMAKE_EXECUTABLE_SUFFIX}
+                        -DCMAKE_CXX_COMPILER=${HOST_TOOLCHAIN_DIR}/clang-cl${CMAKE_EXECUTABLE_SUFFIX}
+                        -DCMAKE_ASM_COMPILER=${HOST_TOOLCHAIN_DIR}/clang-cl${CMAKE_EXECUTABLE_SUFFIX})
+      if(lld IN_LIST TOOLCHAIN_TOOLS)
+        list(APPEND compiler_args -DCMAKE_LINKER=${HOST_TOOLCHAIN_DIR}/lld-link${CMAKE_EXECUTABLE_SUFFIX})
+      endif()
+      if(llvm-ar IN_LIST TOOLCHAIN_TOOLS)
+        list(APPEND compiler_args -DCMAKE_AR=${HOST_TOOLCHAIN_DIR}/llvm-lib${CMAKE_EXECUTABLE_SUFFIX})
+      endif()
+      if(llvm-mt IN_LIST TOOLCHAIN_TOOLS)
+        list(APPEND compiler_args -DCMAKE_MT=${HOST_TOOLCHAIN_DIR}/llvm-mt${CMAKE_EXECUTABLE_SUFFIX})
+      endif()
+      if(llvm-rc IN_LIST TOOLCHAIN_TOOLS)
+        list(APPEND compiler_args -DCMAKE_RC_COMPILER=${HOST_TOOLCHAIN_DIR}/llvm-rc${CMAKE_EXECUTABLE_SUFFIX})
+      endif()
+    else()
+      set(compiler_args -DCMAKE_ASM_COMPILER=${CMAKE_ASM_COMPILER}
+                        -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
+                        -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
+                        -DCMAKE_LINKER=${CMAKE_LINKER}
+                        -DCMAKE_AR=${CMAKE_AR}
+                        -DCMAKE_RANLIB=${CMAKE_RANLIB}
+                        -DCMAKE_NM=${CMAKE_NM}
+                        -DCMAKE_OBJCOPY=${CMAKE_OBJCOPY}
+                        -DCMAKE_OBJDUMP=${CMAKE_OBJDUMP}
+                        -DCMAKE_STRIP=${CMAKE_STRIP}
+                        -DCMAKE_READELF=${CMAKE_READELF}
+                        -DCMAKE_RC_COMPILER=${CMAKE_RC_COMPILER}
+                        -DCMAKE_MT=${CMAKE_MT})
+    endif()
   endif()
+  message(NOTICE "extproj compiler_args is ${compiler_args}")
   if(CMAKE_CROSSCOMPILING)
     set(llvm_config_path ${LLVM_CONFIG_PATH})
 
diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -77,6 +77,12 @@
 
   set_enable_per_target_runtime_dir()
 
+  message(NOTICE "builtin target for default")
+  #message(NOTICE "cmake args ${CMAKE_ARGS}")
+  message(NOTICE "cmake common args ${COMMON_CMAKE_ARGS}")
+  message(NOTICE "extra args:")
+  message(NOTICE ${BUILTINS_CMAKE_ARGS})
+
   llvm_ExternalProject_Add(builtins
                            ${compiler_rt_path}/lib/builtins
                            DEPENDS ${ARG_DEPENDS}
@@ -111,6 +117,12 @@
     endif()
   endforeach()
 
+  message(NOTICE "builtin target for ${target}")
+  #message(NOTICE "cmake args ${CMAKE_ARGS}")
+  message(NOTICE "cmake common args ${COMMON_CMAKE_ARGS}")
+  message(NOTICE "extra args:")
+  message(NOTICE ${${target}_extra_args})
+
   llvm_ExternalProject_Add(builtins-${target}
                            ${compiler_rt_path}/lib/builtins
                            DEPENDS ${ARG_DEPENDS}
@@ -221,6 +233,13 @@
 
   set_enable_per_target_runtime_dir()
 
+  message(NOTICE "runtime target for default")
+  #message(NOTICE "cmake args ${CMAKE_ARGS}")
+  message(NOTICE "cmake common args ${COMMON_CMAKE_ARGS}")
+  message(NOTICE "extra args:")
+  message(NOTICE ${RUNTIMES_CMAKE_ARGS})
+  message(NOTICE ${ARG_CMAKE_ARGS})
+
   llvm_ExternalProject_Add(runtimes
                            ${CMAKE_CURRENT_SOURCE_DIR}/../../runtimes
                            DEPENDS ${ARG_DEPENDS}
@@ -349,6 +368,12 @@
 
   set_enable_per_target_runtime_dir()
 
+  message(NOTICE "runtime target for ${target}")
+  #message(NOTICE "cmake args ${CMAKE_ARGS}")
+  message(NOTICE "cmake common args ${COMMON_CMAKE_ARGS}")
+  message(NOTICE "extra args:")
+  message(NOTICE ${${name}_extra_args})
+
   llvm_ExternalProject_Add(runtimes-${name}
                            ${CMAKE_CURRENT_SOURCE_DIR}/../../runtimes
                            DEPENDS ${${name}_deps}