lib: helping compiler with early returns

lib/defines.h

@@ -25,7 +25,10 @@
  * Error codes.
  */
 #define kr_ok() 0
-#define kr_error(x) -abs(x)
+/* Mark as cold to mark all branches as unlikely. */
+static inline int __attribute__((__cold__)) kr_error(int x) {
+	return -abs(x);
+}
 #define kr_strerror(x) strerror(abs(x))
 
 /*