[CMake stdlib] do not override flags for RelWithDebInfo when ...

...building the stdlib for Apple platforms.

For now we want to match the flags the existing configuration (which is
already accounted by the default values provided by CMake) -- in
particular the generation of full symbols and usage of whole module
optimization.

Addresses rdar://142620659

Author: edymtt

Runtimes/Core/cmake/caches/Vendors/Apple/apple-common.cmake

@@ -12,7 +12,3 @@ set(SwiftCore_ENABLE_VECTOR_TYPES ON CACHE BOOL "")
 set(SwiftCore_ENABLE_RUNTIME_FUNCTION_COUNTERS ON CACHE BOOL "")
 set(SwiftCore_ENABLE_BACKDEPLOYMENT_SUPPORT ON CACHE BOOL "")
 set(SwiftCore_ENABLE_FILESYSTEM_SUPPORT ON CACHE BOOL "")
-
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O3 -gline-tables-only -DNDEBUG" CACHE STRING "")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO "-O3 -gline-tables-only -DNDEBUG" CACHE STRING "")
-set(CMAKE_Swift_FLAGS_RELWITHDEBINFO "-O -gline-tables-only" CACHE STRING "")