With many components disabled, configuration checked for many programs and
compiler flags that weren't actually used for anything.  This is slow, and
makes simple builds look a lot more complicated than they are.  So, rework
things to only check for tools and flags that will actually be used.

Mainly this is to make the package nice to use as a subproject.

The less time wasted with manual code formatting, the better.

Fedora takes issue with CC0.  Although it doesn't really matter for this
stuff (dual licensed anyway, questionably "software", certainly not patentable,
and so on), this is simpler and more consistent with the ISC license used for
the actual software anyway.

Older versions of Doxygen warn about these.  So, remove them to make the build
less noisy since they are all either unused or set to their defaults anyway.

These all have the default value anyway.