bug#43501: gst-plugins-bad cannot be built on linux-armhf, breaking qemu

[Mark H Weaver <mhw@netris.org>]

Earlier, I wrote:
> Ever since 'spice-gtk' was added, it has included *every* gstreamer
> plugin package in its 'propagated-inputs'.

On my private branch, I removed 'gst-libav', 'gst-plugins-bad' and
'gst-plugins-ugly' from the propagated-inputs of 'spice-gtk'.

--8<---------------cut here---------------start------------->8---
diff --git a/gnu/packages/spice.scm b/gnu/packages/spice.scm
index 4aff8dbf56..4b4c673a9d 100644
--- a/gnu/packages/spice.scm
+++ b/gnu/packages/spice.scm
@@ -144,11 +144,8 @@ which allows users to view a desktop computing environment.")
     (build-system gnu-build-system)
     (propagated-inputs
       `(("gstreamer" ,gstreamer)
-        ("gst-libav" ,gst-libav)
         ("gst-plugins-base" ,gst-plugins-base)
         ("gst-plugins-good" ,gst-plugins-good)
-        ("gst-plugins-bad" ,gst-plugins-bad)
-        ("gst-plugins-ugly" ,gst-plugins-ugly)
         ("spice-protocol" ,spice-protocol)
 
         ;; These are required by the pkg-config files.
--8<---------------cut here---------------end--------------->8---

I rebuilt my system and user profiles with this patch applied, and
everything seems to work fine.  Moreover, I'm glad to report that
'gst-plugins-ugly' is no longer in my store.  (Sadly, 'gst-plugins-bad'
still is, because our 'gnome' package depends on 'cheese' which depends
on 'gst-plugins-bad', and last I checked that was unavoidable.)

I haven't tried using the 'spice' functionality specifically, but I
suspect that any reduced "out-of-the-box" functionality could be
regained by users simply installing those plugins as needed, along with
gstreamer for its 'native-search-paths' field.

What do you think?

      Mark

PS: Danny's idea is worth considering in its own right, but I think it's
    orthogonal to this proposed change.