[PCH] When writing out the list of input files, avoid emitting duplicate
entries of the same file.

This can happen because the file was "included" multiple times and is
referenced by multiple SLocEntries.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169829 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed