Eliminate the redundancy between source-file information in the source

Eliminate the redundancy between source-file information in the source
manager block and input-file information in the control block. The
source manager entries now point back into the control block. Input
files are now lazily deserialized (if validation is disabled). Reduces
Cocoa's PCH by the ~70k I added when I introduced the redundancy in
r166251.

llvm-svn: 166429