Make the gc descriptor tests fail consistently if python is not found.
Fix monodis compilation on mingw which is missing some fp classification functions.
Fix mingw compilation problems.
Remove the usage of gcc-3 on mingw, the gcc-3 package no longer exists on cygwin. Mono can be built by configuring with --host=i686-pc-mingw32. Building without this will not work, since the libtool wrapper executables created by libtool will be unusable, i.e. they exit before the real runtime process exits.