[Bug-gsl] Building DLLs on Windows

[P]

Hi there,

I believe there is a slight typo in gsl_types.h

Where it should be "#ifdef _WIN32"
Source
https://docs.microsoft.com/en-us/previous-versions/visualstudio/visual-studio-2008/b0084kay(v=vs.90)

Without this change DLLs do not build.

Secondly, it seems a large number of functions are missing the prefix
"GSL_VARS" and cannot be used in DLLs built by MSVC.

More information on this can be found here:
https://github.com/ampl/gsl/issues/24#issuecomment-503330162

Kind regards
Philip Deegan
https://github.com/Dekken