Fix Base.StackTraces.lookup(C_NULL - 1) on macOS 12 (#43612)
See comment in diff for explanation. This fixes test/stacktraces.jl
on aarch64 macOS 12, and according to an OpenJDK issue where they
ran into the same problem, https://git.openjdk.java.net/jdk/pull/6193,
probably also x86_64 macOS 12.
