In SourceManager::getFileIDLoaded(), add some sanity checks to make sure we don't enter an infinite loop.

rdar://13120919

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@176331 91177308-0d34-0410-b5e6-96231b3b80d8
[PCH] Enhance InputFile to also include whether the file is out-of-date.

Previously we would return null for an out-of-date file. This inhibited ASTReader::ReadSLocEntry
from creating a FileID to recover gracefully in such a case.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@176332 91177308-0d34-0410-b5e6-96231b3b80d8
Add one more sanity check in SourceManager::getFileIDLoaded().

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@176333 91177308-0d34-0410-b5e6-96231b3b80d8