RFC: Add _dl_x86_cpu_features to rtld_global for x86

[H.J. Lu]

Hi,

I created hjl/cpuid/master branch to move x86 cpu_features
to rtld_global. I initialize _dl_x86_cpu_features before
__libc_start_main.  It simplifies IFUNC support on x86.  Any
comments?

Thanks.

-- 
H.J.