WasmLLVMRuntimeLibs: respect `args.build_runtime_with_host_compiler` (#82949)
This allows quickly building `WasmLLVMRuntimeLibs` product with the host toolchain (usually Swift nightly development snapshot toolchain) when `--skip-build-llvm --skip-build-swift --build-runtime-with-host-compiler` combination of options is passed to `build-script`.