[libunwind] [libunwind] Add CMake option to enable execute-only code generation on AArch64 (PR #140554)

[Csanád Hajdú via cfe-commits]

Il-Capitano wrote:

I simplified the configuration based on the discussion in the RFC. C and C++ compiler flags will be handled by the change in https://github.com/llvm/llvm-project/pull/143698.

https://github.com/llvm/llvm-project/pull/140554