3b2: Fix Coverity identified issues

This change also addresses some unused function parameter warnings
issued by GNU Flycheck (not generally used by the build process, but
useful when editing files with Flycheck enabled)

3B2/3b2_defs.h

@@ -56,6 +56,9 @@ noret __libc_longjmp (jmp_buf buf, int val);
 #ifndef MIN
 #define MIN(x,y) ((x) < (y) ? (x) : (y))
 #endif
+#ifndef UNUSED
+#define UNUSED(x)  ((void)((x)))
+#endif
 
 /* -t flag: Translate a virtual address */
 #define EX_T_FLAG 1 << 19