build: Fix build with multiarch
Submitted by Jeremy Bicha
On Debian-based distros, gnome-builder 3.26.0 installs the Ide.py file to /usr/lib/x86_64-linux-gnu/python3/dist-packages/gi/overrides/Ide.py
This causes the Jedi plugin to fail because that path isn't part of PYTHONPATH.
The correct location is /usr/lib/python3/dist-packages/gi/overrides/Ide.py
mbiebl proposed the following patch with the comment "that code is obviously false for multi-arch, not sure why that check is needed at all"
This bug is a regression introduced with the port to meson (didn't affect Ubuntu 17.04's gnome-builder 3.24 which didn't build with meson)