Bugfix: Include unistd.h needed for ssize_t type

fpgautils.h

@@ -12,6 +12,7 @@
 
 #include <stdbool.h>
 #include <stdio.h>
+#include <unistd.h>
 
 typedef bool(*detectone_func_t)(const char*);
 typedef char(*autoscan_func_t)();