main/musl: epoll syscall cancelation point patch

Patch created by @dalias

https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/899#note_865199

closes #12528 (closed)

If someone looks for better source of patch: https://git.musl-libc.org/cgit/musl/commit/?id=2c00f95c1ac7dd50f53d9e361847ebd2513c8da0 (Just found it in upstream tree)