x86: Don't include <x86intrin.h>

Use __builtin_ia32_rdtsc directly since including <x86intrin.h> makes
building glibc very slow.  On Intel Core i5-6260U, this patch reduces
x86-64 build time from 8 minutes 33 seconds to 3 minutes 48 seconds
with "make -j4" and GCC 8.2.1.

	* sysdeps/x86/hp-timing.h: Don't include <x86intrin.h>.
	(HP_TIMING_NOW): Replace _rdtsc with __builtin_ia32_rdtsc.