Added extern "C" if __cplusplus is defined.

diff --git a/include/shellapi.h b/include/shellapi.h
index 4291a47..90e9352 100644
--- a/include/shellapi.h
+++ b/include/shellapi.h
@@ -3,6 +3,10 @@
 
 #include "windef.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif /* defined(__cplusplus) */
+
 #include "pshpack1.h"
 
 /******************************************
@@ -264,6 +268,10 @@
 BOOL      WINAPI ShellAboutW(HWND,LPCWSTR,LPCWSTR,HICON);
 #define     ShellAbout WINELIB_NAME_AW(ShellAbout)
 
+#ifdef __cplusplus
+} /* extern "C" */
+#endif /* defined(__cplusplus) */
+
 #include "poppack.h"
 
 #endif /* _WINE_SHELLAPI_H */