support #include'ing from c++ compiles

include/margo.h

@@ -7,6 +7,10 @@
 #ifndef __MARGO
 #define __MARGO
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #include <mercury_bulk.h>
 #include <mercury.h>
 #include <mercury_macros.h>
@@ -115,4 +119,8 @@ hg_return_t __name##_handler(hg_handle_t handle) { \
  */
 #define DECLARE_ARGO_RPC_HANDLER(__name) hg_return_t __name##_handler(hg_handle_t handle);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* __MARGO */