Support 'stub' wglGetExtensionsStringEXT function.

dlls/opengl32/make_opengl

@@ -517,6 +517,7 @@ print SPEC "@  stdcall wglCreateContext(long) wglCreateContext
 @  stdcall wglDescribeLayerPlane(long long long long ptr) wglDescribeLayerPlane
 @  stdcall wglGetCurrentContext() wglGetCurrentContext
 @  stdcall wglGetCurrentDC() wglGetCurrentDC
+@  stdcall wglGetExtensionsStringEXT() wglGetExtensionsStringEXT
 @  stdcall wglGetLayerPaletteEntries(long long long long ptr) wglGetLayerPaletteEntries
 @  stdcall wglGetProcAddress(str) wglGetProcAddress
 @  stdcall wglMakeCurrent(long long) wglMakeCurrent

dlls/opengl32/opengl32.spec

@@ -5,6 +5,7 @@
 @  stdcall wglDescribeLayerPlane(long long long long ptr) wglDescribeLayerPlane
 @  stdcall wglGetCurrentContext() wglGetCurrentContext
 @  stdcall wglGetCurrentDC() wglGetCurrentDC
+@  stdcall wglGetExtensionsStringEXT() wglGetExtensionsStringEXT
 @  stdcall wglGetLayerPaletteEntries(long long long long ptr) wglGetLayerPaletteEntries
 @  stdcall wglGetProcAddress(str) wglGetProcAddress
 @  stdcall wglMakeCurrent(long long) wglMakeCurrent

dlls/opengl32/wgl.c

@@ -644,6 +644,15 @@ static BOOL process_attach(void)
   return TRUE;
 }
 
+/* Some WGL extensions... */
+static const char *WGL_extensions = "";
+
+const char * WINAPI wglGetExtensionsStringEXT(void) {
+    TRACE("() returning \"%s\"\n", WGL_extensions);
+
+    return WGL_extensions;
+}
+
 static void process_detach(void)
 {
   glXDestroyContext(default_display, default_cx);