native::start should get a more accurate estimate of the stack bounds

[huonw]

It currently just assumes that it's always 2MB.

This logic was added by #11360.

[alexcrichton]

On linux (and possibly other related unices), we can use getrlimit(RLIMIT_STACK) to learn a bit about the stack limit.

[steveklabnik]

native::start is now totally gone, so I believe this is now irrelevant.

[jshs]

The stack size of the main thread is still estimated in std::rt, so I think the issue remains relevant.

[pnkfelix]

reopening: the code in question is still just guessing, AFAICT, and appears to be triggering an overflow (or underflow) panic on the branch with arithmetic overflow checking: http://buildbot.rust-lang.org/builders/auto-linux-32-opt/builds/3910/steps/test/logs/stdio

[steveklabnik]

Triage: the FIXME comment is now gone, and I don't know the internals well enough to determine if this is something that's still relevant. I think the removal of morestack would have made this go away?

[alexcrichton]

Ah yeah this is long since gone