Keep compatibility with MS PSDK ddraw.h file by using WINNT instead of
_WINNT_ in the preprocessor conditional test.
Incidentally this allows also removing those #define NT_BUILD_ENVIRONMENT
in the win32ss modules.
See commit 5fcfaf2e1 (r42346).
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.
