Makefile: set default goals in makefiles

Makefile: set default goals in makefiles

Explicitly set the default goal at the very top of various makefiles.
This is already present in some makefiles, but not all of them.

In particular, this corrects a regression introduced in a38edab7c8
(Makefile: generate doc versions via GIT-VERSION-GEN, 2024-12-06).  That
commit added some config files as build targets for the Documentation
directory, and put the target configuration in a sensible place.
Unfortunately, that sensible place was above any other build target
definitions, meaning the default goal changed to being those
configuration files only, rather than the HTML and man page
documentation.

Signed-off-by: Adam Dinwoodie <adam@dinwoodie.org>
Helped-by: Junio C Hamano <gitster@pobox.com>
Acked-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>