[llvm] [CMake][Runtimes] Set LLVM_RUNTIMES_BUILD before HandleLLVMOptions (PR #194495)

[Jinsong Ji via llvm-commits]

jsji wrote:

Thanks @jhuber6 and @petrhosek .  The situation is that we need to remove some build options we added LLVMOptions that are not applicable to runtimes into HandleLLVMOptions. I am fine with abandoning this given the direction to move awasy from using HandleLLVMOptions.

https://github.com/llvm/llvm-project/pull/194495