[compiler-rt] [compiler-rt] fix __sanitizer::struct_sock_fprog_sz availability (PR #118762)

[via llvm-commits]

Zentrik wrote:

I'm getting an error 
```
[09:12:16] /workspace/srcdir/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cpp:493:35: error: invalid application of ‘sizeof’ to incomplete type ‘__sanitizer::sock_fprog’
[09:12:16]   493 |   unsigned struct_sock_fprog_sz = sizeof(struct sock_fprog);
[09:12:16]       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~
[09:12:16] In file included from /workspace/srcdir/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_posix.h:20,
[09:12:16]                  from /workspace/srcdir/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_libignore.cpp:16:
```

https://github.com/llvm/llvm-project/pull/118762