GCC-7 and glibc-2.27 compat code

Summary:

• Use IN6ADDR_ANY_INIT instead of in6addr_any
• Remove C style cast in net.cpp
• Add stdin, stdout, stderr to ignored export list

Test Plan:

make check

Reviewers: #bitcoin_abc, schancel

Reviewed By: #bitcoin_abc, schancel

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1882