Make the PNaCl driver accept additional arguments.
Make the PNaCl driver accept additional arguments.

This CL is part of work to allow Emscripten to use PNaCl as its toolchain.  The
main change is to implement the -Xclang and -nostdinc++ arguments.  A less
significant change is to accept arguments that PNaCl sets by default  (-m32,
-emit-llvm, -target le32-unknown-nacl).

BUG= none
R=dschuff@chromium.org

Review URL: https://codereview.chromium.org/19377002

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@11785 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client