The test uses an erroneous non-directive within #ifdef _WIN32 to
signal that _WIN32 is defined. Some compilers choke on this even when
_WIN32 isn't defined. Observed with FreeBSD 4.10's gcc 2.95.4.
Broken in commit c02468fd, v4.3.22. Standaline client build already
broken in commit 774b590f, v4.3.17.
Use an unmatched brace instead.
Checking Windows libraries with autoconf is cumbersome, because
linking often fails unless you include the header, and AC_SEARCH_LIBS
doesn't permit that.
Just detect the Windows API instead, with new MY_WINDOWS_API.
