[compiler-rt] [llvm] Reland check-builtins target for LLVM_ENABLE_RUNTIMES (PR #171941)

[Andrew Haberlandt via llvm-commits]

ndrewh wrote:

@petrhosek Have you had a chance to diagnose the armhf failures you were seeing with this change? I had a hypothesis [here](https://github.com/llvm/llvm-project/pull/166837#issuecomment-3645339732) but I don't have a setup for building the armhf configuration so I haven't been able to test anything myself.

https://github.com/llvm/llvm-project/pull/171941