With fortification enabled, few function calls return result need to be
checked, has they get the __wur macro enabled.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

	in loop to look for conversion specifier to avoid testing of
	wrong errno value.
	* stdio-common/Makefile (tests): Add bug18, bug18a, bug19, bug19a.
	* stdio-common/bug18a.c: New file.
	* stdio-common/bug19.c: New file.
	* stdio-common/bug19a.c: New file.