x11-libs/gdk-pixbuf: Uprev to 2.42.6

Also pull in meson-multilib.eclass from upstream commit
5bf2727139974d789e1a3b3a10d3a6e85ffd6c62

BUG=chromium:1215974
TEST=emerge-eve x11-libs/gdk-pixbuf

Change-Id: Ia3642d0b0c655a003b6da3a1bc0874b2cc7e326c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/2939904
Tested-by: Fergus Dall <sidereal@google.com>
Commit-Queue: Fergus Dall <sidereal@google.com>
Reviewed-by: David Munro <davidmunro@google.com>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Nicholas Verne <nverne@chromium.org>
5 files changed