[llvm] AArch64: Move outline atomic libcalls configuration (PR #144374)

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic approved this pull request.

We might eventually want some mechanism that scans the module to see if, for example, there are any functions that might call the outlined atomic routines.  A linker could use this to minimize the number of objects we pull into the link.  But this is fine for now.

https://github.com/llvm/llvm-project/pull/144374