Do we need "DEFINES=-DWIN32 -DGSL_DLL" in the Makefile of the gsl package?

[Julien Bect]

Hi all,

A long time ago (2007...) Michael Goffioul added the following line to 
the Makefile of the gsl package:

DEFINES=
ifeq ($(canonical_host_type),i686-pc-msdosmsvc)
DEFINES=-DWIN32 -DGSL_DLL
endif

These lines are still here:

https://sourceforge.net/p/octave/gsl/ci/11467a9d9e122abc2e5546ab79b9640daf8e11f8/tree/src/Makefile.in

but I have no idea idea if they are still relevant.

I assume this is for building directly on windows (as opposed to 
cross-compiling) but I have no idea if this is really possible...

I am very close to finally making a new release of the package, and I 
was wondering if these lines should be preserved or removed...

If they are to be preserved, it would be nice to add a comment 
explaining why they are useful.

@++
Julien