[CMake][runtimes] Process common options in runtimes build

This was removed in D39932 but turned out this is actually needed
because runtimes such as compiler-rt and libc++ rely on common options
processing for setting certain flags such as -ffunction-sections and
-fdata-sections.

Differential Revision: https://reviews.llvm.org/D45507

llvm-svn: 329778

runtimes/CMakeLists.txt

@@ -107,6 +107,13 @@ if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR})
     endif()
   endif()
 
+  # Avoid checking whether the compiler is working.
+  set(LLVM_COMPILER_CHECKED ON)
+
+  # Handle common options used by all runtimes.
+  include(AddLLVM)
+  include(HandleLLVMOptions)
+
   set(CMAKE_REQUIRED_FLAGS ${SAFE_CMAKE_REQUIRED_FLAGS})
   set(CMAKE_REQUIRED_LIBRARIES ${SAFE_CMAKE_REQUIRED_LIBRARIES})