gccrs: respect the unify rules commit flag

gccrs: respect the unify rules commit flag

We use the types compatable interface for unify here and so if
we dont respect the commit flag the interface can have unintended
side effects with infer type hints throwing things off down the line.

gcc/rust/ChangeLog:

	* typecheck/rust-unify.cc (UnifyRules::expect_inference_variable): dont commit
	(UnifyRules::expect_adt): likewise
	(UnifyRules::expect_bool): likewise
	(UnifyRules::expect_char): likewise
	(UnifyRules::expect_int): likewise
	(UnifyRules::expect_uint): likewise
	(UnifyRules::expect_float): likewise
	(UnifyRules::expect_isize): likewise
	(UnifyRules::expect_usize): likewise

Signed-off-by: Philip Herron <herron.philip@googlemail.com>