vpx: Error out if enabled and no features found

See: gstreamer/cerbero#200
22 jobs for backport-mr-381-into-1.16-error-vpx-no-features in 55 minutes and 21 seconds (queued for 14 seconds)
Status Job ID Name Coverage
  Preparation
passed #920842
gst indent

00:03:15

passed #920874
manifest

00:02:59

failed #920841
manifest

00:06:14

 
  Build
passed #920851
build cerbero android universal

00:09:18

passed #920852
build cerbero cross win32

00:05:16

passed #920853
build cerbero cross win64

00:09:41

passed #920850
build cerbero fedora x86_64

00:06:31

passed #920855
gst-ios-12.2
build cerbero ios universal

00:39:37

passed #920854
gst-macos-10.14
build cerbero macos x86_64

00:09:24

passed #920843
build fedora x86_64

00:04:41

passed #920849
1607 windows docker
build msys2

00:11:39

passed #920844
build nodebug fedora x86_64

00:02:58

passed #920845
build static fedora x86_64

00:10:38

passed #920846
build static nodebug fedora x86_64

00:02:56

passed #920847
1607 windows docker
build vs2017 amd64

00:09:28

passed #920848
1607 windows docker
build vs2017 x86

00:10:07

 
  Test
passed #920856
gstreamer
check fedora

00:04:27

passed #920857
gstreamer
integration testsuites fedora

00:08:34

passed #920859
gstreamer
valgrind bad

00:06:16

passed #920860
gstreamer
valgrind ges

00:04:53

passed #920858
gstreamer
valgrind good

00:06:55

 
  Integrate
passed #920861
android universal examples

00:07:22