CI: Downgrade to llvm-8

.gitlab-ci.yml

@@ -101,7 +101,7 @@ static:cppcheck:
 static:clang-tidy:
   <<: *static_template
   script:
-    - jq ".[].file" release/compile_commands.json | tr -d "\"" | grep -v "test-src" | xargs -n1 -P$(grep -c processor /proc/cpuinfo) clang-tidy-9 -p release/
+    - jq ".[].file" release/compile_commands.json | tr -d "\"" | grep -v "test-src" | xargs -n1 -P$(grep -c processor /proc/cpuinfo) clang-tidy-8 -p release/
 # -----------------------------------------------
 # build
@@ -126,7 +126,7 @@ build:builder:clang:
   <<: *config_builder
   <<: *template_build
   variables:
-    CXX: clang++-9
+    CXX: clang++-8
 build:arch:
   <<: *config_arch