[lldb] Honor the CPU type & subtype when launching on macOS

Honor the CPU type (and subtype) when launching the inferior on macOS.

Part of this functionality was thought to be no longer needed and
removed in 85bd4369, however it's still
needed, for example to launch binaries under Rosetta 2 on Apple Silicon.

This patch will use posix_spawnattr_setarchpref_np if available and
fallback to posix_spawnattr_setbinpref_np if not.

Differential revision: https://reviews.llvm.org/D95922