std.Build: Demote errors for exceeding max_rss to warnings.

We have no control over memory usage on arbitrary systems in the wild. But we
would still like to get the warnings so we can adjust the values based on
observations in the official ZSF CI.

Closes #23254.
Closes #23638.

lib/compiler/build_runner.zig

@@ -599,7 +599,6 @@ fn prepare(
             if (run.max_rss_is_default) {
                 std.debug.print("note: use --maxrss to override the default", .{});
             }
-            return uncleanExit();
         }
     }
 }

lib/std/Build/Step.zig

@@ -247,7 +247,6 @@ pub fn make(s: *Step, options: MakeOptions) error{ MakeFailed, MakeSkipped }!voi
             s.result_peak_rss, s.max_rss,
         }) catch @panic("OOM");
         s.result_error_msgs.append(arena, msg) catch @panic("OOM");
-        return error.MakeFailed;
     }
 }