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

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Is it really a problem to require a compiler at that point?  I mean, you need a compiler to build compiler-rt.builtins anyway.

The problem with a libc-free compiler-rt.builtins is that it's missing functionality.  Assuming libc specifically doesn't depend on that functionality, I guess you could build a compiler-rt.builtins specifically for building libc, install it separately, build libc, then immediately build the real compiler-rt.builtins.  But that multiplies the compiler-rt configurations in exchange for... not having to install libc headers?

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