Use mpiifx, mpicx, mpicpx instead of mpiifort, mpiicc, mpiicpc

[Micket]

easybuild-framework/easybuild/toolchains/mpi/intelmpi.py

Lines 64 to 68 in b37f707

	self.MPI_COMPILER_MPICC = 'mpiicc'
	self.MPI_COMPILER_MPICXX = 'mpiicpc'
	self.MPI_COMPILER_MPIF77 = 'mpiifort'
	self.MPI_COMPILER_MPIF90 = 'mpiifort'
	self.MPI_COMPILER_MPIFC = 'mpiifort'

Since ifort, icc, icpc are going away, I think we should probably use the new binaries for these as well.
I'm not sure how we deal with change here. I guess we should check the intel compiler version and just make it conditional?