Options 1 and 2 were  defined as follows :

> (1) Enable the warning (pragma) in Fl_SVG_Image.cxx just before we
> include the nanosvg headers and (maybe [1]) disable it afterwards.
>
> (2) Use a new file just for the nanosvg implementation (maybe
> fl_nanosvg.cxx?) and use the #pragma before the inclusion of nanosvg
> headers (no restore needed [1]).

Therefore I'm a little confused when I read

  "option[s] (1: extra implementation file) "

My vote would be for

"Enable the warning (pragma) in Fl_SVG_Image.cxx and disable it afterwards"

with the advantage of not introducing a new file with very little added value.

But, is it possible that some older versions of Visual Studio don't support

#pragma warning (push) / #pragma warning (pop)

In that case, option

"Use a new file just for the nanosvg implementation"

would be my choice.