[clang] [lldb] [llvm] Remove some `try_compile` CMake checks for compiler flags (PR #92953)

[Chris Apple via cfe-commits]

cjappl wrote:

Thanks for your help! You were correct that cc was pointing to gcc. This is fixed when I updated my machine to use my known clang as the default compiler.

For future archeologists, this meant (from [this answer](https://askubuntu.com/questions/1198087/how-to-set-clang-9-as-the-default-c-compiler-on-ubuntu-19-10))

```
sudo update-alternatives --install /usr/bin/c++ c++ /usr/bin/clang++ 60
sudo update-alternatives --install /usr/bin/cc cc /usr/bin/clang 60
```

https://github.com/llvm/llvm-project/pull/92953