Fix for SPACK-35: Fortran not working properly

- Spack needed symlinks in env for fortran compilers.
- 'fc' is a bash bulitin, so can't use it for fortran compiler.
  - switched to 'f90' for this.

- mpich 3 builds with fortran now.
  - enabled shared libs in mpich package

var/spack/packages/mpich/package.py

@@ -38,6 +38,8 @@ class Mpich(Package):
     provides('mpi@:1', when='@1:')
 
     def install(self, spec, prefix):
-        configure("--prefix=" + prefix)
+        configure(
+            "--prefix=" + prefix,
+            "--enable-shared")
         make()
         make("install")