compiler: recognize Go 1.18 runtime/internal/atomic methods

compiler: recognize Go 1.18 runtime/internal/atomic methods

The Go 1.18 library introduces specific types in runtime/internal/atomic.
Recognize and optimize the methods on those types, as we do with the
functions in runtime/internal/atomic.

While we're here avoid getting confused by methods in any other
package that we recognize specially.

	* go-gcc.cc (Gcc_backend::Gcc_backend): Define builtins
	__atomic_load_1 and __atomic_store_1.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/383654