[PATCH][AArch64] Use builtins for fpcr/fpsr

[Wilco Dijkstra]

Joseph Myers wrote:
  
In file included from ../include/fpu_control.h:2:0,
                 from test-fpucw.c:19:
../sysdeps/aarch64/fpu/fpu_control.h:24:5: error: "__GNUC_PREREQ" is not defined, evaluates to 0 [-Werror=undef]

> fpu_control.h is missing an include of features.h, as needed to use 
> __GNUC_PREREQ.

Yes, I added the include but forgot to merge it with the patch. Now committed.

Wilco