[compiler-rt] [TSan] Fix warning when compiling with -Wmissing-designated-field-initializers (PR #163401)

[Dan Blackwell via llvm-commits]

https://github.com/DanBlackwell created https://github.com/llvm/llvm-project/pull/163401

Currently we receive a warning when initializing a ThreadEventCallbacks when compiling with this flag:
```
llvm-project/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp:252:3: warning: missing field 'start' initializer [-Wmissing-designated-field-initializers]
  252 |   };
      |   ^
```

This patch explicitly initializes the missing fields to null, fixing the warning.

rdar://162074310

>From df4993eac8d03a7fde617d0edd4cd1bc245dcd1f Mon Sep 17 00:00:00 2001
From: Dan Blackwell <dan_blackwell at apple.com>
Date: Tue, 14 Oct 2025 15:06:32 +0100
Subject: [PATCH] [TSan] Fix warning when compiling with
 -Wmissing-designated-field-initializers

Currently we receive a warning when initializing a ThreadEventCallbacks when compiling with this flag:
```
llvm-project/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp:252:3: warning: missing field 'start' initializer [-Wmissing-designated-field-initializers]
  252 |   };
      |   ^
```

This patch explicitly initializes the missing fields to null, fixing the warning.
---
 compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp b/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp
index 62ab0554df08e..7fa5e017d3985 100644
--- a/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp
+++ b/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp
@@ -259,7 +259,9 @@ void InitializePlatform() {
 
   ThreadEventCallbacks callbacks = {
       .create = ThreadCreateCallback,
+      .start = nullptr,
       .terminate = ThreadTerminateCallback,
+      .destroy = nullptr,
   };
   InstallPthreadIntrospectionHook(callbacks);
 #endif