OS X regression fix
Unfortunately, !10 (merged) GLIBC changes broke Mac OS X build again. This change fixes the OS X build.
From Felix:
It breaks on macOS, because __GLIBC_PREREQ is evaluated though __GLIBC__ is not defined. Splitting it into two #if lines makes things work again. The change to the __xmknod dev pointer argument checks also broke.
Edited by Ilya Lipnitskiy