gitignore: ignore multiple output directories
Developers may have multiple output directories when building multiple
boards in parallel. A previous commit attempted to gitignore new output
directories automatically but broke some things (commit a14c862c08
"Create a .gitignore file in the CANONICAL_O directory").
To provide some support, ignore anything in the Buildroot directory that
starts with "output". This is a bit more cumbersome, but doesn't break
packages based on Python maturin.
Signed-off-by: Brandon Maier <brandon.maier@collins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>