run through the 'C' preprocessor. That is pick up the file name
and line numbers from the cpp hash file line comments for the
dwarf file and line numbers tables.
rdar://9275556
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167237 91177308-0d34-0410-b5e6-96231b3b80d8