tinycc: fix paxmark call

I missed this due to testing on a checkout that didn't contain
the paxmark fix ...

pkgs/development/compilers/tinycc/default.nix

···
   checkTarget = "test";
 
   postFixup = ''
-    paxmark m $out/bin/tcc
+    paxmark m $bin/bin/tcc
   '';
 
   meta = {