fix umount2 compilation for alpha on Linux 5.x
fix umount2 compilation for alpha on Linux 5.x

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