mariadb: Disable parallel building again

It still fails intermittently on lex_token.h.

http://hydra.nixos.org/build/33571559

pkgs/servers/sql/mariadb/default.nix

@@ -64,7 +64,7 @@ stdenv.mkDerivation rec {
   ];
 
   # fails to find lex_token.h sometimes
-  enableParallelBuilding = true;
+  enableParallelBuilding = false;
 
   outputs = [ "out" "lib" ];