Remove C++ guard before forwarder declarations.

mingw-w64-headers/include/sti.h

diff --git a/mingw-w64-headers/include/sti.h b/mingw-w64-headers/include/sti.h
index e9ac31e..4b5b5f3 100644
--- a/mingw-w64-headers/include/sti.h
+++ b/mingw-w64-headers/include/sti.h
@@ -264,11 +264,9 @@
 
 #define STI_RAW_RESERVED 0x1000
 
-#ifdef __cplusplus
   struct IStillImageW;
   struct IStillImageA;
   struct IStiDevice;
-#endif
 
   STDMETHODIMP StiCreateInstanceW(HINSTANCE hinst,DWORD dwVer,struct IStillImageW **ppSti,LPUNKNOWN punkOuter);
   STDMETHODIMP StiCreateInstanceA(HINSTANCE hinst,DWORD dwVer,struct IStillImageA **ppSti,LPUNKNOWN punkOuter);