Bug #344007 accept4 syscall unhandled on arm64 (242) and ppc64 (344)

ppc64 might fall back to socketcall in some cases, but arm64 always uses
accept4 syscall directly. Some (confusing) background on when/how glibc
(wrongly) decides to use a direct accept4 or the socketcall system call:
https://sourceware.org/ml/libc-alpha/2013-12/msg00014.html

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14926 a5019735-40e9-0310-863c-91ae7b9d1cf9
3 files changed