The PR shows that we ICE after lexing an invalid unterminated raw string,
because lex_raw_string() pops the main buffer unexpectedly. Resolve by
handling this case the same way as for other directives.

libcpp/ChangeLog:
	PR preprocessor/117118
	* lex.cc (lex_raw_string): Treat an unterminated raw string the same
	way for a deferred pragma as is done for other directives.

gcc/testsuite/ChangeLog:
	PR preprocessor/117118
	* c-c++-common/raw-string-directive-3.c: New test.
	* c-c++-common/raw-string-directive-4.c: New test.