Enable EBX for x86 in 32bits PIC code

[Florian Weimer]

On 08/28/2014 03:01 PM, Uros Bizjak wrote:
> I'd like to avoid X86_TUNE_RELAX_PIC_REG and always treat EBX as an
> allocatable register. This way, we can avoid all mess with implicit
> xchgs in atomic_compare_and_swap<dwi>_doubleword. Also, having
> allocatable EBX would allow us to introduce __builtin_cpuid builtin
> and cleanup cpiud.h.

It also makes writing solid inline assembly which has to use %ebx for 
some reason much easier.  We just fixed a glibc bug related to that.

-- 
Florian Weimer / Red Hat Product Security