Summary:
After a remark on a FreeBSD mailing list that the clang man page did
not have any list of possible values for the `-std=` flag, I have now
attempted to exhaustively list those, for each available language.
I also documented the default standard for each language, if there was
more than one choice.
Reviewers: rsmith, dexonsmith, sylvestre.ledru, mgorny
Reviewed By: rsmith
Subscribers: fhahn, emaste, cfe-commits, krytarowski
Differential Revision: https://reviews.llvm.org/D45406
llvm-svn: 329827