[CMake] Make bootstrap and compiler-rt depend on cxx-headers.

Since r334468, we no longer always copy the libcxx headers by virtue of
their presence when cmake runs.

This makes some of the later stages (compiler-rt, and the bootstrapped
stages) depend on them being copied, via the cxx-headers target.

Differential Revision: https://reviews.llvm.org/D48700

llvm-svn: 335898

clang/CMakeLists.txt

@@ -621,10 +621,15 @@ if (CLANG_ENABLE_BOOTSTRAP)
     LLVM_ENABLE_PROJECTS
     LLVM_ENABLE_RUNTIMES)
 
-  # We don't need to depend on compiler-rt if we're building instrumented
+  # We don't need to depend on compiler-rt/libcxx if we're building instrumented
   # because the next stage will use the same compiler used to build this stage.
-  if(TARGET compiler-rt AND NOT LLVM_BUILD_INSTRUMENTED)
-    add_dependencies(clang-bootstrap-deps compiler-rt)
+  if(NOT LLVM_BUILD_INSTRUMENTED)
+    if(TARGET compiler-rt)
+      add_dependencies(clang-bootstrap-deps compiler-rt)
+    endif()
+    if(TARGET cxx-headers)
+      add_dependencies(clang-bootstrap-deps cxx-headers)
+    endif()
   endif()
 
   set(C_COMPILER "clang")

clang/runtime/CMakeLists.txt

@@ -58,8 +58,12 @@ if(LLVM_BUILD_EXTERNAL_COMPILER_RT AND EXISTS ${COMPILER_RT_SRC_ROOT}/)
     endif()
   endforeach()
 
+  if(TARGET cxx-headers)
+    set(COMPILER_RT_LIBCXX_DEPENDENCY "cxx-headers")
+  endif()
+
   ExternalProject_Add(compiler-rt
-    DEPENDS llvm-config clang
+    DEPENDS llvm-config clang ${COMPILER_RT_LIBCXX_DEPENDENCY}
     PREFIX ${COMPILER_RT_PREFIX}
     SOURCE_DIR ${COMPILER_RT_SRC_ROOT}
     STAMP_DIR ${STAMP_DIR}