gitlab-ci: build RADV in meson-testing

This requires to bump LLVM to 8 because it's the minimum supported
version by RADV.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 2249272..4db40a3 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -229,7 +229,7 @@
     GALLIUM_ST: >
       -D dri3=true
     GALLIUM_DRIVERS: "swrast"
-    LLVM_VERSION: "7"
+    VULKAN_DRIVERS: amd
     BUILDTYPE: "debugoptimized"
   script:
     - .gitlab-ci/meson-build.sh