ci: Add clang build scripts

Adds scripts that instruct CI to build yuzu with the installed Clang
compiler on yuzuemu/build-environments:linux-fresh.

These scripts are based on the .ci/scripts/linux scripts, minus AppImage
building since that isn't necessary. Re-uses linux-fresh since that
container has Clang 12 installed.

.ci/templates/build-standard.yml

@@ -12,6 +12,9 @@ jobs:
       windows:
         BuildSuffix: 'windows-mingw'
         ScriptFolder: 'windows'
+      clang:
+        BuildSuffix: 'clang'
+        ScriptFolder: 'clang'
       linux:
         BuildSuffix: 'linux'
         ScriptFolder: 'linux'
@@ -24,4 +27,4 @@ jobs:
     parameters:
       artifactSource: 'false'
       cache: $(parameters.cache)
-      version: $(parameters.version)
+      version: $(parameters.version)