Log Message:
parallel/mpi-ch: make this build and install on NetBSD.

 * AI_V4MAPPED is not defined on NetBSD, so conditionalize its use.
 * Force the use of pkgsrc GCC (here we require >= gcc 10) so that
   <ISO_Fortran_binding.h> is made available to the C compiler.
 * Sort PLIST.

The result builds and installs on amd64 and i386, but not on powerpc
due to Fortran's "real128" not being available there (CPU limitation).