Remove extraneous space in MSVC-style diagnostic output
There was an extra space between the file location and the diagnostic
/tmp/a.c(1,12): warning: unused parameter 'unused'
the tests didn't catch this due to FileCheck not running in --strict-whitespace mode.
Reported by Marco: http://lists.llvm.org/pipermail/cfe-dev/2019-February/061326.html
Differential revision: https://reviews.llvm.org/D58377