If you keep rebuilding Emacs from the Git repository using just the
"make -jN" commands, to track the development branches, after some time
loaddefs.el becomes outdated. To see the outdated parts, rename
loaddefs.el and then say
$ make -C lisp autoloads-force
Then compare the old loaddefs.el with the newly created one: you will
see many changes, depending on when was the last time you bootstrapped
or otherwise regenerated loaddefs.el from scratch.
This happens because regeneration of the parts of loaddefs.el affected
by Lisp changes is unreliable and misses some changes, in particular
those where autoloads from some Lisp files are redirected to private
*-loaddefs.el files instead of the common loaddefs.el.
These updates should happen automatically, they should not require
people to "make bootstrap" or manually regenerate loaddefs.el.