QHostInfo: adapt to glibc 2.26 no longer requiring us to res_init

From the announcement[1]
  - The GNU C Library will now detect when /etc/resolv.conf has been
    modified and reload the changed configuration.  The new resolver
    option “no-reload” (RES_NORELOAD) disables this behavior.

Since glibc can do it, we don't have to call res_init before every
single getaddrinfo() call. And since we don't need to call res_init, we
don't need to load libresolv.so at all, until we need res_ninit.

We won't do it even if the user configured "no-reload" in
/etc/resolv.conf or RES_NORELOAD in the res variable -- let's assume
that it is the intent, like when /etc/resolv.conf is known to never
change.

[1] https://sourceware.org/ml/libc-alpha/2017-08/msg00010.html

Change-Id: I3868166e5efc45538544fffd14d738d40c375fd1
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

0 files changed, 0 insertions, 0 deletions