[compiler-rt] pass target triple to `check_assembler_flag` (PR #188521)

[Simon Tatham via llvm-commits]

https://github.com/statham-arm approved this pull request.

LGTM, thank you!

Now you point this out, I have no idea why it _did_ work for me. Possibly the clang I was using was configured with Arm as its default target triple?

https://github.com/llvm/llvm-project/pull/188521