Use X extern "C" guards around function declarations for public header

include/X11/extensions/XKBcommon.h

@@ -30,6 +30,7 @@ authorization from the authors.
 
 #include <X11/X.h>
 #include <X11/Xdefs.h>
+#include <X11/Xfuncproto.h>
 #include <X11/keysymdef.h>
 #include <X11/extensions/XKBstrcommon.h>
 #include <X11/extensions/XKBgeomcommon.h>
@@ -51,6 +52,8 @@ typedef struct _XkbcDesc {
     XkbGeometryPtr      geom;
 } XkbcDescRec, *XkbcDescPtr;
 
+_XFUNCPROTOBEGIN
+
 extern char *
 XkbcKeysymToString(KeySym ks);
 
@@ -155,4 +158,6 @@ XkbcAtomGetString(Atom atom);
 extern Atom
 XkbcInternAtom(char *name, Bool onlyIfExists);
 
+_XFUNCPROTOEND
+
 #endif /* _XKBCOMMON_H_ */