Always run C compiler with -fsyntax-only
Always run C compiler with -fsyntax-only

Summary:
buck #infer flavor doesn't rely on .o files so we don't need to generate them.
It will save memory/IO and possibly time

Reviewed By: jvillard, martinoluca

Differential Revision: D3379463

fbshipit-source-id: 1d48f7a

xennygrimmato/infer,jvillard/infer,blzq/infer,facebook/infer,kageiit/infer,jvillard/infer,jsachs/infer,facebook/infer,xennygrimmato/infer,jvillard/infer,ryoon/infer,blzq/infer,jvillard/infer,jvillard/infer,blzq/infer,ryoon/infer,blzq/infer,ryoon/infer,kageiit/infer,facebook/infer,jsachs/infer,xennygrimmato/infer,jvillard/infer,ropas/infer,ryoon/infer,facebook/infer,ryoon/infer,ryoon/infer,jsachs/infer,blzq/infer,blzq/infer,kageiit/infer,xennygrimmato/infer,xennygrimmato/infer,kageiit/infer,jsachs/infer,kageiit/infer,facebook/infer,ropas/infer,kageiit/infer,facebook/infer,jvillard/infer,ropas/infer,ropas/infer,kageiit/infer,jsachs/infer,xennygrimmato/infer,xennygrimmato/infer,facebook/infer,jsachs/infer,ropas/infer,ropas/infer