Move the set of files to be validated in an AST file into the control

block, so the input files are validated early on, before we've
committed to loading the AST file. This (accidentally) fixed a but
wherein the main file used to generate the AST file would *not* be
validated by the existing validation logic.

At the moment, this leads to some duplication of filenames between the
source manager block and input-file blocks, as well as validation
logic. This will be handled via an upcoming patch.

llvm-svn: 166251