gnuplot on 64-bit Windows, again

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

Follow-up to my posting of July 24: I now have a mingw64 build 
of gnuplot that works correctly on Windows 8. Encouraged by 
this I'm re-posting my patch set. It's smaller this time 
because I'm skipping the changes that Ethan (very reasonably) 
didn't like. (These were designed to hush compiler warnings 
stemming from a perverse Microsoft API rather than any real 
problem in the gnuplot code.)

All my changes are bracketed by ifdef _WIN64, so they 
shouldn't affect any other builds.

Besides patches to the C code I had to do two things to get a 
working build for Windows 8:

1) The file win/wgnuplot.exe.manifest specifies the 
processorArchitecture as "X86". For an x86_64 build this must 
be changed to "amd64" (or wgnuplot.exe won't start). The 
manifest file is included by win/wgnuplot.rc. I've modified 
wgnuplot.rc so that it includes an alternative manifest file, 
wgnuplot.exe.manifest64, if the symbol _WIN64 is defined. (The 
alternative file simply substitutes "amd64" for "X86" in two 
places. To support ming64, wgnuplot.exe.manifest64 should be 
added to the repository.)

2) For the symbols needed for HTML Help support, I tried using 
a 64-bit version of htmlhelp.lib from the current Windows SDK. 
The linker choked on this, with some weird error messages. 
Googling reveals that htmlhelp.lib is some sort of glue or 
shim, and the real business is done by hhctrl.ocx. So I took a 
copy of the 64-bit hhctrl.ocx from Windows 8, used pexports to 
create a .def file, then used mingw64's dlltool to create an 
import library, hhctrl.dll.a. I modified the mingw Makefile, 
substituting "-lhhctrl.dll" for "-lhtmlhelp". The linker was 
then happy and HTML help works OK.

There's nothing in my patch set pertaining to point 2), at 
this point it's just a heads-up for anyone trying a mingw64 
build.

-- 
Allin Cottrell
Department of Economics
Wake Forest University, NC