meson: Don't try to find gio-unix on Windows
Actually gio-unix
is useless on Windows. This MR is to fix gst-build
with pre-installed glib on Windows.
|Subproject glib is buildable: NO (disabling)
|Dependency gio-unix-2.0 from subproject subprojects\glib found: NO
subprojects\gst-plugins-base\meson.build:255:0: ERROR: Could not find dependency libgmodule_dep in subproject glib