Bug 5858; fix on 0.2.3.12-alpha

This commit is completely mechanical; I used this perl script to make it:

 #!/usr/bin/perl -w -i.bak -p

 if (/^\s*\#/) {
     s/MS_WINDOWS/_WIN32/g;
     s/\bWIN32\b/_WIN32/g;
 }

We'll still need to tweak it so that it looks for includes and
libraries somewhere more sensible than "where we happened to find
them on Erinn's system"; so that tests and tools get built too;
so that it's a bit documented; and so that we actually try running
the output.

Work done with Erinn Clark.