c-family: Add <time.h> names to diagnostics for known headers

c-family: Add <time.h> names to diagnostics for known headers

gcc/c-family/ChangeLog:

	* known-headers.cc (get_stdlib_header_for_name): Add <time.h>
	names.

gcc/testsuite/ChangeLog:

	* g++.dg/spellcheck-stdlib.C: Check <ctime> types and functions.

(cherry picked from commit d489ec082ea214109ff54071410f8cd00344e654)