[clang] Do not instrument the rtti_proxies under hwasan

We run into a duplicate symbol error when instrumenting the rtti_proxies
generated as part of the relative vtables ABI with hwasan:

```
ld.lld: error: duplicate symbol: typeinfo for icu_71::UObject
(.rtti_proxy)
>>> defined at brkiter.cpp
>>>
arm64-hwasan-shared/obj/third_party/icu/source/common/libicuuc.brkiter.cpp.o:(typeinfo
for icu_71::UObject (.rtti_proxy))
>>> defined at locavailable.cpp
>>>
arm64-hwasan-shared/obj/third_party/icu/source/common/libicuuc.locavailable.cpp.o:(.data.rel.ro..L_ZTIN6icu_717UObjectE.rtti_proxy.hwasan+0xE00000000000000)
```

The issue here is that the hwasan alias carries over the visibility and
linkage of the original proxy, so we have duplicate external symbols
that participate in linking. Similar to D132425 we can just disable
hwasan for the proxies for now.

Differential Revision: https://reviews.llvm.org/D132691