build runner: don't incorrectly omit reference traces

It's incorrect to ever set `include_reference_trace` here, because the
compiler has already given or not given reference traces depending on
the `-freference-trace` option propagated to the compiler process by
`std.Build.Step.Compile`.

Perhaps in future we could make the compiler always return the reference
trace when communicating over the compiler protocol; that'd be more
versatile than the current behavior, because the build runner could, for
instance, show a reference trace on-demand without having to even invoke
the compiler. That seems really useful, since the reference trace is
*often* unnecessary noise, but *sometimes* essential. However, we don't
live in that world right now, so passing the option here doesn't make
sense.

Resolves: ziglang#23415

Author: mlugg

lib/compiler/build_runner.zig

@@ -750,7 +750,7 @@ fn runStepNames(
     if (run.prominent_compile_errors and total_compile_errors > 0) {
         for (step_stack.keys()) |s| {
             if (s.result_error_bundle.errorMessageCount() > 0) {
-                s.result_error_bundle.renderToStdErr(.{ .ttyconf = ttyconf, .include_reference_trace = (b.reference_trace orelse 0) > 0 });
+                s.result_error_bundle.renderToStdErr(.{ .ttyconf = ttyconf });
             }
         }
 
@@ -1129,11 +1129,7 @@ fn workerMakeOneStep(
         defer std.debug.unlockStdErr();
 
         const gpa = b.allocator;
-        const options: std.zig.ErrorBundle.RenderOptions = .{
-            .ttyconf = run.ttyconf,
-            .include_reference_trace = (b.reference_trace orelse 0) > 0,
-        };
-        printErrorMessages(gpa, s, options, run.stderr, run.prominent_compile_errors) catch {};
+        printErrorMessages(gpa, s, .{ .ttyconf = run.ttyconf }, run.stderr, run.prominent_compile_errors) catch {};
     }
 
     handle_result: {