Eliminate a race condition with the global module index.

Essentially, a module file on disk could change size between the time
we stat() it and the time we open it, and we need to be robust against
such a problem.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174529 91177308-0d34-0410-b5e6-96231b3b80d8
Accept and ignore the -fextended-identifiers option.

This was GCC's option to turn on UCN support, which we always have on now
in C99 and C++ modes.

Additionally, mark the -fno-extended-identifiers option as unsupported,
since we don't support disabling UCNs in C99 and C++ modes.

PR11538

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174530 91177308-0d34-0410-b5e6-96231b3b80d8