fix for gcc 2.96 and current CVS

Here is a patch to get current CVS compiling with an older gcc (2.96):

Index: state.c
===================================================================
RCS file: /cvsroot/winex/dlls/d3dgl/state.c,v
retrieving revision 1.39
diff -r1.39 state.c
364a365
>     DWORD enabled, enable;
366,367c367,368
<     DWORD enabled = priv->isClipPlaneEnabled;
<     DWORD enable = state ^ enabled;
---
>     enabled = priv->isClipPlaneEnabled;
>     enable = state ^ enabled;