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

Index: backend/gt68xx_low.c
--- backend/gt68xx_low.c.orig
+++ backend/gt68xx_low.c
@@ -52,6 +52,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <errno.h>
 
 #ifdef USE_FORK
 #include <sys/wait.h>