Globally silence all Wattribute warnings

Globally silence all Wattribute warnings

Instead of playing a game of whack-a-mole, disable any -Wattribute
warnings globally. This means, people won't get the warnings when
building with older compilers which lack certain attributes.

Thus we can remove the _Pragma. With that gone, we no longer need the
clang-format off segment.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/376
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>