[cmake] Also pass CMAKE_ASM_COMPILER_ID to next stage when bootstrapping

Summary:
When setting CMAKE_ASM_COMPILER=clang, we also need to set
CMAKE_ASM_COMPILER_ID=Clang.

This is needed because cmake won't set CMAKE_ASM_COMPILER_ID if
CMAKE_ASM_COMPILER is already set.

Without CMAKE_ASM_COMPILER_ID, cmake can't set
CMAKE_ASM_COMPILER_OPTIONS_TARGET either, which means
CMAKE_ASM_COMPILER_TARGET is ignored, causing cross compiling to fail,
i.e., `--target=${CMAKE_ASM_COMPILER_TARGET}` isn't passed.

Differential Revision: https://reviews.llvm.org/D42232

llvm-svn: 322977