Suppress LLVM static test on Arch

It is properly detected as unavailable, ever since commit
d1b783f

Author: eli-schwartz

test cases/frameworks/15 llvm/test.json

@@ -7,7 +7,7 @@
         { "val": "combination", "skip_on_jobname": ["msys2"] }
       ],
       "link-static": [
-        { "val": true, "skip_on_jobname": ["opensuse", "linux-gentoo-gcc"] },
+        { "val": true, "skip_on_jobname": ["arch", "opensuse", "linux-gentoo-gcc"] },
         { "val": false }
       ]
     }