fix(bench): separate vlibc-under-test TU from host harness TUs

benchmarks/bench_string.c

@@ -149,5 +149,14 @@ main(void)
         printf("%llu\n", sink);
     }
 
+    /*
+     * Explicit flush: this harness is a host program, but under
+     * --with-libc=vlibc its DT_NEEDED order puts libvlibc.so before
+     * libc.so.6, so the exit() that runs at process end is vlibc's — which
+     * does not flush stdio yet (that hook lands with the stdio todo).
+     * Without the flush the timed results above are lost.
+     */
+    fflush(stdout);
+
     return 0;
 }