gccrs: intrinsics: Add unchecked operation intrinsics

gcc/rust/ChangeLog:

	* backend/rust-compile-intrinsic.cc (is_basic_integer_type): New function.
	(unchecked_op_inner): New handler.
	(unchecked_op_handler): New handler.

gcc/testsuite/ChangeLog:

	* rust/compile/torture/intrinsics-6.rs: New test.
	* rust/compile/torture/intrinsics-7.rs: New test.