x86: Make the GDT_ENTRY() macro in <asm/segment.h> safe for assembly

Make the GDT_ENTRY() macro in  <asm/segment.h> safe for use in
assembly code by guarding the ULL suffixes with _AC() macros.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
LKML-Reference: <4D5DFBE4.7090104@intel.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Matthieu Castet <castet.matthieu@free.fr>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>