fstat: make new code aarch64 specific
fstat: make new code aarch64 specific

The new code get's used by MIPS64 N64 and fails.
Make the new code aarch64 specific.

kraj/uclibc-ng,wbx-github/uclibc-ng,wbx-github/uclibc-ng,wbx-github/uclibc-ng,kraj/uclibc-ng,wbx-github/uclibc-ng,kraj/uclibc-ng,kraj/uclibc-ng