Add missing qualifiers to the global variable.

opal/runtime/opal_params.h

@@ -30,7 +30,7 @@ extern char *opal_signal_string;
 extern char *opal_net_private_ipv4;
 extern char *opal_set_max_sys_limits;
 
-int opal_verbs_want_fork_support;
+OPAL_DECLSPEC extern int opal_verbs_want_fork_support;
 
 #if OPAL_ENABLE_TIMING
 extern char *opal_timing_sync_file;