testsuite: Add --status to runtest invocation

testsuite: Add --status to runtest invocation

By default, if a test driver (a test .exp) ends with an uncaught
error/exception, the runtest command will still have a return code of 0
(success).  However, if a test (or the environment) is broken and does
not work properly, it should be considered as failed so that we can
notice it and fix it.

Passing the --status flag to runtest will make it return an error if one
of the test it runs ends up with an uncaught error.

gdb/testsuite/ChangeLog:

	* Makefile.in (check-single): Pass --status to runtest.
	(check/%.exp): Likewise.