Updated __poll_chk implementation to be not so strict

[mxaddict]

This fixes a crash for navcoin-qt when libs call poll() with bad data.

Updated the __poll_chk to behave less aggressive (More like __explicit_bzero_chk)

Calls __chk_fail() instead of an assert which would terminate the execution of the rest of the app

[mxaddict]

@marcus290 this is a fix for the issue you found.

[mxaddict]

Basically I copied logic from glibc: https://sourceware.org/git/?p=glibc.git;a=blob;f=debug/poll_chk.c;h=34596de9777b3fe9f05e8a57840dd75076c51672;hb=HEAD

[aguycalled]

Where do the original changes from d3b5687#diff-626fe822220cf08b83b6459ec6c2b29b which introduced the bug come from?

[mxaddict]

glob_old, wrap_glob and __wrap_glob64 I coded based on the __wrap_log2f code that was already in the file.

__poll_chk I based on glibc implementation, but I used assert (I did not know __chk_fail existed) : https://sourceware.org/git/?p=glibc.git;a=blob;f=debug/poll_chk.c;h=34596de9777b3fe9f05e8a57840dd75076c51672;hb=HEAD

__explicit_bzero_chk I based on monero implementation: https://github.com/monero-project/monero/blob/master/src/common/compat/glibc_compat.cpp

reallocarray from : libunbound in our ./depends dir

getentropy I think I coded myself.

[mxaddict]

I updated my commit to also remove the header for assert

[aguycalled]

Tested debian

[proletesseract]

building in ubuntu 18.04

[marcus290]

Tested on a 64-bit Linux gitian build on Ubuntu. Not getting the crash anymore