Build errors for glibc version greater than 2.26

[dhrvg]

Hi,

SIGUNUSED is synonymous with SIGSYS, and is no longer available since glibc version 2.26 and is causing build errors. I think it can be removed from the signals initializer_list<> in reckless/src/crash_handler.cpp.

Thanks.

[mattiasflodin]

Resolved in c1d0932.