glibc support for allocating alternate signal stacks

[Florian Weimer]

I've posted a proposal to provide an interface for allocating stacks
in glibc:

  Misc: Add <sys/cstack.h> and the cstack_* family of functions
  <https://sourceware.org/pipermail/libc-alpha/2021-May/126608.html>

This is based on our observation that many applications use static
buffers for alternate stacks, which is not thread-safe.

I'd appreciate If you could comment here or on libc-alpha based on your
experience with alternate signal stacks.

Thanks,
Florian