fenv: only allow to enable for supported architectures
fenv: only allow to enable for supported architectures

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