Let's have the makefiles cry with very old compiler versions

[stenczelt]

TLDR

Apparently (some) very old compilers cannot build QUIP, as we are using stuff that was not supported in gfortran say ~9 years ago. Makes sense. Is there an easy way to complain in the makefiles if the detected compiler version is below a specified version that we last tested?

What I know so far is that gfortran 4.8.5 will not do the trick.

More details

The issue came in from someone trying to install QUIP+GAP with CASTEP and failing as:

/[..path removed..]/QUIP/src/libAtoms/MPI_context.f95:63.43:

character(len=:), allocatable :: hostname
                                         1
Error: Deferred-length character component 'hostname' at (1) is not yet supported
/[..path removed..]/QUIP/src/libAtoms/MPI_context.f95:63.43:

character(len=:), allocatable :: hostname
                                         1
Error: Deferred-length character component 'hostname' at (1) is not yet supported
make[1]: *** [MPI_context.o] Error 1
make[1]: Leaving directory `/[..path removed..]/QUIP/build/linux_x86_64_gfortran_openmp'
make: *** [libAtoms] Error 2

gfortran --version:

GNU Fortran (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44)
Copyright (C) 2015 Free Software Foundation, Inc.

[gabor1]

We can just update the docs