checkpatch: emit an error when using predefined timestamp macros

Since commit fe7c36c7

 ("Makefile: Build with -Werror=date-time if
the compiler supports it"), use of __DATE__, __TIME__, and __TIMESTAMP__
has not been allowed.

As this test is gcc version specific (> 4.9), it hasn't prevented a few
new uses from creeping into the kernel sources.

Make checkpatch complain about them.

Signed-off-by: Joe Perches <joe@perches.com>
Original-patch-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>