There is no need to compile our DLLs as shared libraries since we are
managing symbols exports and imports through spec files.
On my system, this reduces the configure-time by a factor of two.
- Make sure the DWLP_* values are correct on _WIN64
- Don't use the DWL_* constants, they are not portable. Enforce this by removing them entirely from winuser.h
- Make sure Get/SetWindowLong*Ptr* is used and pointers are not truncated to LONG