[objcmt] If the frontend option is frontend::MigrateSource then we don't need to create
the arcmt wrappers.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194627 91177308-0d34-0410-b5e6-96231b3b80d8
[objcmt] Transfer the objcmt flags from the driver to cc1 invocation and
instantiate ObjCMigrateASTConsumer with the specific options that were enabled.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194628 91177308-0d34-0410-b5e6-96231b3b80d8
[objcmt] If no objcmt options were specified, default to enable literals+subscripting.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194629 91177308-0d34-0410-b5e6-96231b3b80d8