gitlab-ci: Prune all SCons jobs except scons-win64, and allows failures.

Based on the discussion in https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4352

Reviewed-by: Daniel Stone <daniels@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4363>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4363>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 0cf5f58..a8a29ed 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -437,8 +437,9 @@
 scons-win64:
   extends: .scons-build
   variables:
-    SCONS_TARGET: platform=windows machine=x86_64
+    SCONS_TARGET: platform=windows machine=x86_64 debug=1
     SCONS_CHECK_COMMAND: "true"
+  allow_failure: true
 
 meson-clover:
   extends: .meson-build
@@ -558,22 +559,6 @@
       -Dosmesa=gallium
       --cross-file=.gitlab-ci/x86_64-w64-mingw32
 
-scons:
-  extends: .scons-build
-  variables:
-    SCONS_TARGET: "llvm=1"
-    SCONS_CHECK_COMMAND: "scons force_scons=1 ${SCONS_TARGET} check"
-  script:
-    - SCONS_TARGET="" SCONS_CHECK_COMMAND="scons check force_scons=1" .gitlab-ci/scons-build.sh
-    - LLVM_VERSION=9 .gitlab-ci/scons-build.sh
-
-scons-old-llvm:
-  extends:
-    - scons
-    - .use-x86_build_old
-  script:
-    - LLVM_VERSION=3.9 .gitlab-ci/scons-build.sh
-
 .test:
   extends:
     - .ci-run-policy