Module debugging: Make the module format part of the module hash instead

of the file name. This is consistent with how other HeaderSearchOptions
are handled.

Due to the other inputs of the module hash (revision number) this is not
really testable in a meaningful way.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@257520 91177308-0d34-0410-b5e6-96231b3b80d8