swprintf_s in src/win32

[Allin C. <cot...@wf...>]

Three of the source files in gnuplot's src/win32 use the function 
swprintf_s(), namely wgdiplus.cpp, wmenu.c and wtext.c. In one of 
these files, wgdiplus.cpp, there's a recognition that this function 
is not universally available:

#ifdef __WATCOMC__
// swprintf_s is missing from <cwchar>
# define swprintf_s(s, c, f, ...) swprintf(s, c, f, __VA_ARGS__)
#endif

It seems to me that this guard against use of an undefined function 
should also be present in wmenu.c and wtext.c. Moreover, it's not 
just the Watcom compiler that's affected: swprintf_s is not declared 
in the headers provided for cross-compilation via mingw64.

Hence, a request: could this back-up definition be provided in all 
the affected files, and could it please be extended from __WATCOM__ 
to some convenient symbol that could be defined on the compiler 
command line for any system that's missing the definition -- for
example something like:

#if defined(__WATCOM__) || defined(SWPRINTF_S_MISSING)
<alternative definition>
#endif

That way, one would not have to hack these three files to get 
current wgnuplot.exe to build.

Thanks.

-- 
Allin Cottrell
Department of Economics
Wake Forest University