This is the clang driver part of the change to embedded bitcode. This
- -fembed-bitcode option which breaks down the compilation into two
stages. The first stage emits optimized bitcode and the second stage
compiles bitcode into object file.
- -fembed-bitcode-marker option which doesn't really break down to
two stages to speedup the compilation flow.
- pass the correct linker flag to darwin linker if tool chains supports