[PCH] Store the offsets of source location file entries and go through them
in ASTReader::validateFileEntries().

This avoids going through all source location entries and fixes the performance regression.
Many thanks to Doug for the hint!
(rdar://9530587)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@132481 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed