[gjs/june-maintenance] CI: Fix image builds

[Philip Chimento <pchimento src gnome org>]

commit 0d10efacf89be9a9dd23a3b2baaac67b63d58d44
Author: Philip Chimento <philip chimento gmail com>
Date:   Sun Jul 5 07:08:12 2020 -0700

    CI: Fix image builds
    
    Apparently llvm-config has been moved into a package that is no longer
    included in mozjs68's build dependencies.

 test/extra/Dockerfile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/test/extra/Dockerfile b/test/extra/Dockerfile
index ae5590c9..b92bfdd1 100644
--- a/test/extra/Dockerfile
+++ b/test/extra/Dockerfile
@@ -6,7 +6,7 @@ ARG BUILD_OPTS=
 
 ENV SHELL=/bin/bash
 
-RUN dnf -y install 'dnf-command(builddep)' git make which
+RUN dnf -y install 'dnf-command(builddep)' git make which llvm-devel
 RUN dnf -y builddep mozjs68
 
 WORKDIR /root