build: split build system into smaller manageable pieces

Split the build system into smaller manageable pieces, grouped by
context. In that sense, we can keep the most important information
within the Makefile itself, and group out misc bits and pieces that
we just include into it. E.g. 'Cmds' contains all defined commands
that we call from other locations, 'Template' contains the generic
build template for all tools, 'Extra' has pieces that need special
treatment for the tools to build and 'Misc' contains help and release
code. This makes it more manageable on the long run. While at it, I
also simplified some code and removed all Wflags expect "-Wall" as
we want to convert into "-Wall -Wextra -W" anyway.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>