helper: wl-socket: fix build for musl
bind(2) expects its second parameters is a "const struct sockaddr*", let's cast the "struct sockaddr_un*" to "struct sockaddr*" before passing into bind(2).
SUN_LEN is a BSD extension that also implemented by GNU, let's define _GNU_SOURCE before including "sys/un.h".
Need to be back-ported to 5.21
There is also another fix for musl, namely: add _GNU_SOURCE
to 3rdparty/xcursor.c
, but I'm not the author of that patch https://github.com/void-linux/void-packages/blob/master/srcpkgs/kwin/patches/musl.patch