I remember trying to build HPL my first time as a student :-) Its much simpler than you think It also is a great way to learn about linking and make files. (Well in my opinion).
See my comments below, mostly quickly looking is you should change g77 and gcc to mpicc.
Yes mpicc calls gcc you can see by running
Thus you can ommit the MPdir, MPinc, and MPlib (No libmpich.a !!!!!)
You can see one I use to ACML on our cluster, note we use PGI compilers.