Print stack overflow messages for Linux and OS X

This installs signal handlers to print out stack overflow messages on Linux. It also ensures the main thread has a guard page.

This will catch stack overflows in external code. It's done in preparation of switching to stack probes (#16012).

I've done some simple tests with overflowing the main thread, native threads and green threads (with and without UV) on x86-64.
This might work on ARM, MIPS and x86-32.

I've been unable to run the test suite on this because of #16305.
This is likely the strategy that we're going to pursue rather than segmented stacks in the future, so it would be nice to have a path forward for filling out these implementations. Have you investigated to see if FreeBSD and Android platforms provide functionality like this, and if so how hard it would be to bind it?

I can help out with any specifics, but it would be nice to see what our path forward here is!