PETSc: use cmake compilers for building PETSc with MPI
this is useful when compiling nektar++ with different compilers as those set in the openMPI config (as mentiones in #18 (closed)) or when using compiler wrappers such as ccache or icecream.
this is useful when compiling nektar++ with different compilers as those set in the openMPI config (as mentiones in #18 (closed)) or when using compiler wrappers such as ccache or icecream.