Add function. Sometimes I don't understand MSDN. This function is
available on Windows XP and Server 2003, but the SDK is supposed to
make it available when _WIN32_WINNT >= 0x0400, or so says the MSDN.
Mmmh...
* include/winbase.h [_WIN32_WINNT >= 0x0400] (CreateFiberEx):
Guard function. Same remark as above.
* lib/user32.def (ConvertFiberToThread, CreateFiberEx):
Add functions.