[Driver] Add support for -finline-functions and /Ob2 flags
-finline-functions and /Ob2 are currently ignored by Clang. The only way to
enable inlining is to use the global O flags, which also enable other options,
or to emit LLVM bitcode using Clang, then running opt by hand with the inline
This patch allows to simply use the -finline-functions flag (same as GCC) or
/Ob2 in clang-cl mode to enable inlining without other optimizations.
This is the first patch of a serie to improve support for the /Ob flags.
Patch by Rudy Pons <email@example.com>!
Differential Revision: http://reviews.llvm.org/D20576