updated win32 macro

[Akim Demaille]

>>>>> "tailbert" == tailbert  <edward> writes:

tailbert> it's a language feature.

OK, but then I fail to understand why you'd need to have WIN32=' ' to
know the test was run.  Either you are looking for a switch for a
language dependent feature, or you look for some support of something
on your system, in which case AC_HEADER_WINDOWS was fine, IMHO.

But Robert says he needs more: be able to make decisions based on
whether windows.h is there or not, and he was suggesting to provide
$WIN32 as a configure interface to HAVE_WINDOWS_H.  Then, it is a host
feature you are looking for, and AC_SYS is the logical answer.