setarch: nicer error message for execvp

src.custom/setarch/setarch.c

@@ -439,7 +439,7 @@ int main(int argc, char **argv) {
             fflush(NULL);
         }
         execvp(argv[0], argv);
-        err(1, "execvp");
+        err(1, "execvp: failed to execute '%s'", argv[0]);
         return 1;
     }