[OHOS aarch64] [compiler-rt] [gwp_asan] Fix pthread_atfork_for_gwpasan link error · Pull Request !655 · OpenHarmony/third_party_llvm-project

### Issue
https://gitee.com/openharmony/third_party_llvm-project/issues/IBERRJ

### Reason (Purpose, Solved Problem)
Fix gwp_asan test cases symbol link error with pthread_atfork_for_gwpasan:

```
[2024-12-30T06:26:03.227Z] ld.lld: error: undefined symbol: pthread_atfork_for_gwpasan
[2024-12-30T06:26:03.227Z] >>> referenced by guarded_pool_allocator_posix.cpp:115 (./out/lib/clangrt-aarch64-linux-ohos/./toolchain/llvm-project/compiler-rt/lib/gwp_asan/platform_specific/guarded_pool_allocator_posix.cpp:115)
[2024-12-30T06:26:03.227Z] >>> guarded_pool_allocator_posix.cpp.o:(gwp_asan::GuardedPoolAllocator::installAtFork()) in archive /home/jenkins/agent/workspace/LLVM/LLVM_ASAN/panda_src/out/llvm-install/lib/clang/15.0.4/lib/aarch64-linux-ohos/libclang_rt.scudo_standalone.a
```

### Description

该接口在musl头文件pthread.h已声明，在使用处声明弱函数指针

### Test (Local test)

```
[0/1] cd /home/gaohongtao/llvm/test-suites/build/test/gwp_asan && /usr/bin/python3.11 /home/gaohongtao/llvm/test-suites/build/bin/llvm-lit -sv /home/gaohongtao/llvm/test-suites/build/test/gwp_asan/AARCH64OHOSConfig
llvm-lit: /home/gaohongtao/llvm/toolchain/llvm-project/compiler-rt/test/lit.common.cfg.py:154: warning: Compiler lib dir != compiler-rt lib dir
Compiler libdir:     "/home/gaohongtao/llvm/out/llvm-install/lib/clang/15.0.4/lib/aarch64-linux-ohos"
compiler-rt libdir:  "/home/gaohongtao/llvm/test-suites/llvm-install/lib/clang/15.0.4/lib/aarch64-linux-ohos"
llvm-lit: /home/gaohongtao/llvm/toolchain/llvm-project/compiler-rt/test/lit.common.cfg.py:175: note: Testing using libraries in "/home/gaohongtao/llvm/out/llvm-install/lib/clang/15.0.4/lib/aarch64-linux-ohos"
-- Testing: 13 tests, 13 workers --
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..

Testing Time: 42.18s
  Passed: 13
```

### Need to cherry-pick to release (eg：monthly_20221018, OpenHarmony-3.2-Beta5 ...) branch？

- [ ] yes，branch list:
- [x] no

why:

###  Compatibility impact assessment, please indicate (N)

类型	指派人员	状态
审查		已完成 (1/1)
测试		已完成 (1/1)

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