c-common.c (check_format_info): Warn for non-constant format strings with strftime...

c-common.c (check_format_info): Warn for non-constant format strings with strftime formats if -Wformat-nonliteral.

	* c-common.c (check_format_info): Warn for non-constant format
	strings with strftime formats if -Wformat-nonliteral.  Where the
	format can convert arguments, if the format is not a string
	literal and there are no arguments to the format, give a different
	warning message from the general non-string-literal case.

testsuite:
	* gcc.dg/format-nonlit-3.c: New test.

From-SVN: r38105