[CodeGen] Restore accessing __stack_chk_guard via a .refptr stub on mingw after 2518433f

Add tests for this particular detail for x86 and arm (similar tests
already existed for x86_64 and aarch64).

The libssp implementation may be located in a separate DLL, and in
those cases, the references need to be in a .refptr stub, to avoid
needing to touch up code in the text section at runtime (which is
supported but inefficient for x86, and unsupported for arm).

Differential Revision: https://reviews.llvm.org/D92738