Fix function naming

Buffers whose names start with a space are “ephemeral”, as by the Emacs
Lisp manual.
Inhibit automatic checks in ephemeral buffers

The user will likely never see these buffers anyway, so there is no
point in automatically checking them
Extract autoloads detection into function
Simplify Emacs Lisp predicates

Make use of the fancy `bound-and-true-p` function and do not explicitly
check for ephemeral compilation buffers (as Flycheck now won't check
ephemeral buffers automatically anyway).