glapi: Add extern "C" to glapi_priv.h

* The Haiku glapi has a C++ wrapper around the dispatch code.

Reviewed-by: Brian Paul <brianp@vmware.com>

src/mapi/glapi/glapi_priv.h

@@ -49,6 +49,10 @@ typedef void *GLeglImageOES;
 #include "glapi/glapi.h"
 
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* getproc */
 
 extern void
@@ -106,4 +110,8 @@ get_entrypoint_address(unsigned int functionOffset);
 #define MAX_EXTENSION_FUNCS 256
 
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif