build: Check for epoll_create1 rather than epoll_create in meson.build

Because `epoll_create1()` is what the code in `giounix-private.c`
actually uses.

Spotted by Xuntao Chi.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Fixes: #3450

meson.build

@@ -677,7 +677,7 @@ functions = [
   'copy_file_range',
   'endmntent',
   'endservent',
-  'epoll_create',
+  'epoll_create1',
   'fallocate',
   'fchmod',
   'fchown',