The pipe2/dup3/accept4 functions and SOCK_CLOEXEC are quite old nowadays
on Linux. They were introduced on Linux 2.6.28 and glibc 2.10, all from
2008. They were also picked up by uClibc in 2011 and FreeBSD as of
version 10.0. So we no longer need the runtime detection of whether the
feature is available.
Instead, if the libc has support for it, use it unconditionally and fail
at runtime if the syscall isn't implemented.
Change-Id: Ib056b47dde3341ef9a52ffff13efcc39ef8dff7d
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
