cpuid: optimize x86 & fix x86_64 truncation

Use xchg on x86 to avoid needing to use an intermediate register and
shave off one instruction.

Skip the whole thing on x86_64 to avoid truncating the top 32bits of
the rbx reg due to moving things around with ebx/etc...

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
ignore gdb state files

Signed-off-by: Mike Frysinger <vapier@gentoo.org>