c-common.c (check_format_types): Check for writing through a NULL pointer argument.

c-common.c (check_format_types): Check for writing through a NULL pointer argument.

	* c-common.c (check_format_types): Check for writing through a
	NULL pointer argument.

testsuite:
	* gcc.dg/c90-printf-1.c, gcc.dg/c90-scanf-1.c: Add tests for
	writing through null pointers; remove comment about testing
	unterminated strings.

From-SVN: r36936