set_cpp_flag affects everything, including 3rd party code.
We need to perform this separation as 3rd party code has unfixed warnings that we want to check for in our code.
This also has the added benefit that we can use build switches (DCHECK_ALWAYS_ON, REACTOR_EMIT_DEBUG_INFO) without requring a full rebuild of LLVM.
Bug: b/130343040
Bug: b/130335507
Change-Id: I577653e8eb3c4e588fc582f324b5ab6095662e54
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/29809Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
