[modules] If we're given a module file, via -fmodule-file=, for a module, but

we can't load that file due to a configuration mismatch, and implicit module
building is disabled, and the user turns off the error-by-default warning for
that situation, then fall back to textual inclusion for the module rather than
giving an error if any of its headers are included.

llvm-svn: 252114