gst-full: improve static app using gstreamer-full and glib

commit 4d49f9f2e719a12cec3099ac55913062ead5b245 Author: Stéphane Cerveau scerveau@collabora.com Date: Mon Oct 26 12:21:39 2020 +0100

gst-full: Use '-Wl,--export-dynamic' in libs private

In a full static link where an app links with gstreamer-full
containing glib embedded (gio). The app must link with
'-Wl,--export-dynamic' to access throurh g_module_open
any symbols such as gst_init_static_plugins.

commit abc1ba849d67925a0e5fec7cd0ce41cdaa4ee88b Author: Stéphane Cerveau scerveau@collabora.com Date: Thu Oct 22 11:55:43 2020 +0200

gst-full: add warning for gst_init_static_plugins

As some compiler might not supported -Wl,--undefined
add a warning to the meson configure stage.