errno.h header is required now that errno is a per-thread variable.
"undefined symbol 'errno'" at runtime with dlopen()'d modules.

Index: backend/genesys/low.cpp
--- backend/genesys/low.cpp.orig
+++ backend/genesys/low.cpp
@@ -21,6 +21,8 @@
 
 #define DEBUG_DECLARE_ONLY
 
+#include <errno.h>
+
 #include "low.h"
 #include "assert.h"
 #include "test_settings.h"