Added EXTERNL definition in netcdf_par.h

[WardF]

• fixes Failure building with mpicc in current master #1507

[edhartnett]

Might be better to have netcdf_par.h #include netcdf.h?

[DennisHeimbigner]

Why should netcdf_par.h be different than e.g. netcdf_mem.h?

[WardF]

Either solution would work; in this case, I’m inclined to err on the side of verbosity. Trying to untangle what has been included, and from where, can be a headache. Or perhaps it’s just me :). I am attracted to the idea that you must include “netcdf.h” if you are working with the ‘default’ NetCDF API.

[edwardhartnett]

Well if you must include netcdf.h when you use netcdf_par.h or netcdf_mem.h, then why not have those files do the work?

The reason it's better is to prevent issues exactly like the one that occurred here.

[DennisHeimbigner]

The rule as added to the include/netcdf_XXX.h files is this:
/*

• In order to use any of the netcdf_XXX.h files, it is necessary
• to include netcdf.h followed by any netcdf_XXX.h files.
• Various things (like EXTERNL) are defined in netcdf.h
• to make them available for use by the netcdf_XXX.h files.
  */

[edwardhartnett]

You are telling people to do something we can do. No one reads the documentation, as you know! ;-)