x86/CPUID: don't use UB shift when library is built as 32-bit

x86/CPUID: don't use UB shift when library is built as 32-bit

At least the insn emulator test harness will continue to be buildable
(and ought to continue to be usable) also as a 32-bit binary. (Right now
the CPU policy test harness is, too, but there it may be less relevant
to keep it functional, just like e.g. we don't support fuzzing the insn
emulator in 32-bit mode.) Hence the library code needs to cope with
this.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>