[libc] [llvm] [LLVM] Replace use of `LLVM_RUNTIMES_TARGET` with `LLVM_DEFAULT_TARGET_TRIPLE` (PR #136208)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

I just turned that error into a warning, the problem is that GCC and LLVM set the triple slightly different and we can't pass `--target=` to GCC like with clang.

https://github.com/llvm/llvm-project/pull/136208