Convert most #ifdef HAVE_FOO checks to #if HAVE_FOO

Convert most #ifdef HAVE_FOO checks to #if HAVE_FOO

The former is somewhat error prone, since the pre-processor will
evaluate the presence of the define, which might have been omitted due
to wrong include or otherwise.

Swap for the other solution we already have in-tree - always set the
relevant define(s) and evaluate them numerically. That combined with
-Wundef means that we'll get meaningful compiler warning when we get
something wrong.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/356
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>