The correct includes for musl are protected by an __GLIBC__ check in the
upstream sources.

Since musl does not provide own defines to identify itself, simply invert
the condition to !__UCLIBC__ in order to fix the build on all libc flavors
supported by OpenWrt.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

Signed-off-by: Marko Ratkaj <marko.ratkaj@sartura.hr>

Signed-off-by: Mislav Novakovic <mislav.novakovic@sartura.hr>