Work around libUV/glib event loop problem

To quote Jameson:
> This is monitoring the kevent for libuv events, but for some reason
> we’re getting back G_IO_NVAL (The file descriptor is not open),
> and we don’t handle errors

src/GLib/signals.jl

@@ -349,7 +349,7 @@ function __init__gmainloop__()
     ccall((:g_source_set_callback, GLib.libglib), Nothing, (Ptr{Nothing}, Ptr{Nothing}, UInt, Ptr{Nothing}),
         src, @cfunction(g_yield, Cint, (UInt,)), 1, C_NULL)
 
-    uv_fd = Sys.iswindows() ? -1 : ccall(:uv_backend_fd, Cint, (Ptr{Nothing},), Base.eventloop())
+    uv_fd = (Sys.iswindows() || Sys.isapple()) ? -1 : ccall(:uv_backend_fd, Cint, (Ptr{Nothing},), Base.eventloop())
     global uv_pollfd = _GPollFD(uv_fd, typemax(Cushort))
     if (uv_pollfd::_GPollFD).fd != -1
         ccall((:g_source_add_poll, GLib.libglib), Nothing, (Ptr{Nothing}, Ptr{_GPollFD}), src, Ref(uv_pollfd::_GPollFD))