Forward CMake options to runtimes builds

[kongyi]

Summary

We specify custom -B in our CMake options, they have to be forwarded to the runtimes builds. Also, OSX target and arch flags need to be passed through to build as universal binary.

[phosek]

This is not the right approach and it'll break common uses of the bootstrapping build since the host flags don't necessarily apply to target, especially when cross-compiling.

llvm/cmake/modules/LLVMExternalProjectUtils.cmake

CMAKE_ARGS ${${nameCanon}_CMAKE_ARGS}
                -DLLVM_USE_RELATIVE_PATHS_IN_FILES=${LLVM_USE_RELATIVE_PATHS_IN_FILES}
                -DLLVM_LIT_ARGS=${LLVM_LIT_ARGS}
                -DLLVM_SOURCE_PREFIX=${LLVM_SOURCE_PREFIX}
                -DPACKAGE_VERSION=${PACKAGE_VERSION}
                -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
                -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
                -DCMAKE_C_COMPILER_LAUNCHER=${CMAKE_C_COMPILER_LAUNCHER}
                -DCMAKE_CXX_COMPILER_LAUNCHER=${CMAKE_CXX_COMPILER_LAUNCHER}
+               -DCMAKE_C_FLAGS=${CMAKE_C_FLAGS}
+               -DCMAKE_CXX_FLAGS=${CMAKE_CXX_FLAGS}
+               -DCMAKE_EXE_LINKER_FLAGS=${CMAKE_EXE_LINKER_FLAGS}
+               -DCMAKE_SHARED_LINKER_FLAGS=${CMAKE_SHARED_LINKER_FLAGS}
+               -DCMAKE_MODULE_LINKER_FLAGS=${CMAKE_MODULE_LINKER_FLAGS}
+               -DCMAKE_OSX_DEPLOYMENT_TARGET=${CMAKE_OSX_DEPLOYMENT_TARGET}
+               -DCMAKE_OSX_ARCHITECTURES=${CMAKE_OSX_ARCHITECTURES}
                -DCMAKE_EXPORT_COMPILE_COMMANDS=1
                ${cmake_args}
                ${PASSTHROUGH_VARIABLES}
     INSTALL_COMMAND ""
     STEP_TARGETS configure build
     BUILD_ALWAYS 1
     USES_TERMINAL_CONFIGURE 1
     USES_TERMINAL_BUILD 1