Here is how you can have FreeFEM reorient the mesh for you.
load "msh3";
lockOrientation = false;
mesh3 Th("pentagono.mesh");
lockOrientation = true;
mesh3 renumbered = Th;
fespace Vh(renumbered, P1);
Vh u = x + y + z;
load "medit"
medit("Th", Th, u);