analyzer: associate -Wanalyzer-va-list-exhausted with CWE-685

analyzer: associate -Wanalyzer-va-list-exhausted with CWE-685

gcc/analyzer/ChangeLog:
	* varargs.cc: Include "diagnostic-metadata.h".
	(va_list_exhausted::emit): Associate the warning with
	CWE-685 ("Function Call With Incorrect Number of Arguments").

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/stdarg-1.c
	(__analyzer_called_by_test_not_enough_args): Verify that
	-Wanalyzer-va-list-exhausted is associated with CWE-685.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>