[metacity] revert "ci: stop using clang for coverity job"

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 5a3d2456df40cd53bd0f7e9135f025799a614f33
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sat Sep 12 15:44:03 2020 +0300

    revert "ci: stop using clang for coverity job"
    
    This reverts commit 1d70b1be2cfdd55f5af3108ec2ddf9f06a960f5a.

 .gitlab-ci.yml | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index ca695b28..205995ba 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -53,22 +53,20 @@ ubuntu:
 coverity:
   image: ubuntu:devel
   stage: analysis
-  variables:
-    # cov-build doesn’t like GLIB_DEPRECATED_ENUMERATOR
-    CFLAGS: '-DGLIB_DISABLE_DEPRECATION_WARNINGS'
   when: manual
   before_script:
     - apt-get update
     - *install-ubuntu-dependencies
     - apt-get install -q -y --no-install-recommends
                       ca-certificates
+                      clang
                       curl
   script:
     - curl https://scan.coverity.com/download/linux64
       --data "token=$COVERITY_TOKEN&project=metacity"
       --output /tmp/coverity_tool.tgz
     - tar zxf /tmp/coverity_tool.tgz
-    - ./autogen.sh --disable-Werror
+    - CC=clang ./autogen.sh --disable-Werror
     - ./cov-analysis-linux64-*/bin/cov-build --dir cov-int make
     - tar czf cov-int.tar.gz cov-int
     - curl --form token=$COVERITY_TOKEN