Remove extraneous space in MSVC-style diagnostic output

There was an extra space between the file location and the diagnostic
message:

  /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

llvm-svn: 354351