xplat: Improve problem handling in PAL

[obastemur]

Claims;

• ChakraCore overall doesn't expect the system calls (i.e. threading) are failing.
• PAL does not do much to mend or provide an interface for it

Things done so far;

• xplat: rand_s fallback #2630 (fallback) and xplat: cache thread stack limit #2679 (cache) are introduced.
• These two fixes help ChakraCore xplat tests to pass under ulimit -n 32

Todo;

• enable testing for limited environment to catch more issues and going forward keep it stable.
• not just open files -n, test for stack size, vm and max memory
• check, if we may have similar issues on Windows under such limitations.

[dilijev]

@digitalinfinity Do we still want to keep this issue around?

[digitalinfinity]

I don't see why not- it's improvements that are worth making to ChakraCore, just not scheduled against any milestone since it's not a bug but a work item. It's something we should get to eventually.