Index: clang/cmake/caches/Fuchsia.cmake
===================================================================
--- clang/cmake/caches/Fuchsia.cmake
+++ clang/cmake/caches/Fuchsia.cmake
@@ -21,6 +21,9 @@
   set(BOOTSTRAP_LLVM_ENABLE_LLD ON CACHE BOOL "")
 endif()
 
+set(CLANG_DEFAULT_CXX_STDLIB libc++ CACHE STRING "")
+set(CLANG_DEFAULT_RTLIB compiler-rt CACHE STRING "")
+
 if(APPLE)
   set(COMPILER_RT_ENABLE_IOS OFF CACHE BOOL "")
   set(COMPILER_RT_ENABLE_TVOS OFF CACHE BOOL "")
@@ -51,6 +54,10 @@
 
 # Setup the bootstrap build.
 set(CLANG_ENABLE_BOOTSTRAP ON CACHE BOOL "")
+set(CLANG_BOOTSTRAP_EXTRA_DEPS
+  builtins
+  runtimes
+  CACHE STRING "")
 set(CLANG_BOOTSTRAP_CMAKE_ARGS
   ${EXTRA_ARGS}
   -C ${CMAKE_CURRENT_LIST_DIR}/Fuchsia-stage2.cmake