Move Enforcer Plugin to 'compile' phase in 'lib'

Move Enforcer Plugin to 'compile' phase in 'lib'

There is a strange effect in Maven builds: Depending on which profiles
are active when building the project - even seemingly unrelated ones
like 'create-docs' or 'clean-libs' - the execution order of plugins in
the 'process-resources' phase can vary. Specifically, Build Helper vs.
Enforcer in module 'lib', which both were in the same phase, can
sometimes be executed in lexical order, which I expected, or the other
way around, which makes the build fail if the existence of the marker
file is checked by Enforcer before Build Helper even had a chance to
create it. Probably, this is because Build Helper is defined inside a
profile and Enforcer outside of any.

Therefore, the safest way to ensure correct ordering of the two is to
place Enforcer in a later phase, in this case 'compile'.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>