[PR93306] Short-circuit has_include

[PR93306] Short-circuit has_include

the preprocessor evaluator has a skip_eval counter, but we weren't
checking it after parsing has_include(foo), but before looking for
foo.  Resulting in unnecessary io for 'FALSE_COND && has_include <foo>'

	PR preprocessor/93306
	* expr.c (parse_has_include): Refactor.  Check skip_eval before
	looking.