There are many reports that sigaltstack() on Apple platforms stops backtrace() from tracing an original stack, e.g. * https://github.com/llvm/llvm-project/commit/d39ead41056b00d10b6223543562cd304307ac9b * https://reviews.llvm.org/D28265 If we disable an alternate stack for signal handler, we won't be able to catch stack overflow errors, but backrace() will work again.
