llvm: bump min version for musl to 11+

Older LLVM versions are not building with musl right now, while 11+
works fine.

pkgs/top-level/all-packages.nix

···
       /**/ if platform.isDarwin then (if platform.isAarch64 then 11 else 7)
       else if platform.isFreeBSD then 7
       else if platform.isAndroid then 12
-      else if platform.isLinux then (if platform.isRiscV then 11 else 7)
+      else if platform.isLinux then
+        /**/ if platform.isRiscV then 11
+        else if platform.isMusl then 11
+        else 7
       else if platform.isWasm then 8
       else latest_version;
     # We take the "max of the mins". Why? Since those are lower bounds of the