Add a SIGSEGV signal handler which detects stack overflow
Add a SIGSEGV signal handler which detects stack overflow

Summary: GuardPageAllocator now keeps a track of all protected pages. If SIGSEGV occurs, signal handler can check address at fault against protected pages and if it matches - we got a fiber stack overflow.

Reviewed By: yfeldblum

Differential Revision: D3386960

fbshipit-source-id: 775b36ee08fecbbd87da0025f794717c222f5cce

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