[Triple] Add Facebook vendor

Add a compiler vendor for Facebook, to enable future vendor-specific
behavior.

Differential Revision: https://reviews.llvm.org/D25136

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287684 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed