With the threading refactoring, loading of object files happens before
checking whether we're dealing with a swift AST. While that's not an
issue per se, it causes a warning to be printed:
warning: /path/to/a.swiftmodule: The file was not recognized as a valid object file
note: while processing /path/to/a.swiftmodule
This suppresses the warning by checking for a Swift AST before
attempting to load is as an object file.
rdar://39240444
llvm-svn: 329553
396e6ea6d7