Proper check for Windows API functions in configure.
Proper check for Windows API functions in configure.

git-svn-id: fe39988874eede3a53f719d8ea44c06d8ae53a4b@8 673e7f9d-eb33-0410-8d51-5d65c45fe375

savonet/dlfcn-win32,Distrotech/dlfn-win32