[compiler-rt] [compiler-rt][AArch64] Enable libc-free builtins Linux build (PR #125922)

[Peter Waller via llvm-commits]

peterwaller-arm wrote:

Since Eli's understanding seems reasonable to me, I'm abandoning unless there is additional pull or justification for this, please comment if so and I will resurrect the thread. I've mentioned that [nixpkgs might want to do the build differently in the future](https://github.com/NixOS/nixpkgs/pull/378713/files#r1947188468), for now they are applying this PR as a patch.

https://github.com/llvm/llvm-project/pull/125922