Warn on va_start() when called with a reference parameter.

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1905.pdf 18.7p3
explicitly calls this (and some other things) out as undefined.

Also move 2 other existing warnings behind the new -Wvarargs flag.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182694 91177308-0d34-0410-b5e6-96231b3b80d8
Make isBeforeInTranslationUnit consistent in the face of failures to get a valid FileID.

Suggested by Jordan.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182695 91177308-0d34-0410-b5e6-96231b3b80d8
Increase the portability of this script a bit: use /usr/bin/env to find bash,
rather than assuming it lives in the path. Patch by Eitan Adler!


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182696 91177308-0d34-0410-b5e6-96231b3b80d8