gccrs: late: Start setting up builtin types

gccrs: late: Start setting up builtin types

gcc/rust/ChangeLog:

	* resolve/rust-late-name-resolver-2.0.cc
	(Late::setup_builtin_types): New function.
	(Late::go): Setup builtin types.
	* resolve/rust-late-name-resolver-2.0.h:
	* resolve/rust-name-resolution-context.cc
	(NameResolutionContext::map_usage): New function.
	* resolve/rust-name-resolution-context.h: Likewise.