Add workaround for older gcc's not fully supporting VISIBLE32.
diff --git a/src/boot.c b/src/boot.c
index 9bbbf07..b090058 100644
--- a/src/boot.c
+++ b/src/boot.c
@@ -208,3 +208,7 @@
     debug_enter(NULL, DEBUG_HDL_19);
     do_boot(0);
 }
+
+// Ughh - some older gcc compilers have a bug which causes VISIBLE32
+// functions to not be exported as a global variables.
+asm(".global handle_18, handle_19");