Revert "Fix missing includes of <errno.h>"
Removing errno from xf86_OSlib.h breaks the xf86-input-mouse driver build. And hw/xfree86/os-support/xf86_OSlib.h itself relies on errno anyway in the SYSCALL macro provided by this header.
This reverts commit f6a36710.
cc @metux, reverts !1416 (merged)
Reference to failing job: https://gitlab.freedesktop.org/xorg/xserver/-/jobs/56455790
Edited by Peter Hutterer