PR16339: Don't produce a diagnostic pointing at the whitespace between a '#if'
and a '!defined(X)' if we find a broken header guard. This is suboptimal; we
should point the diagnostic at the 'X' token not the 'if' token, but it fixes
the crash.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184054 91177308-0d34-0410-b5e6-96231b3b80d8