bug#43678: 27.1; compiler warning if code forgets to require cl-lib

[Stefan Monnier <monnier@iro.umontreal.ca>]

> In bbdb-tex:
> bbdb-tex.el:415:25:Error: Forgot to expand macro cl-progv in (cl-progv ...

Oh, yes, now I can reproduce it as well (I was using an older version
of BBDB before).  And indeed, I had misunderstood the error, this one is
a different one from the one I was thinking of.

This error is because `cl-progv` was not known to the compiler when we
started compiling the `bbdb-tex` function, but during the course of its
compilation, something somewhere caused `cl-lib` to be loaded such that
by the time the byte-compiler gets to look again at (cl-progv ...), it
now notices that it's a macro, which should not be possible because we
should have performed all the macro-expansion at the very
beginning already.

Hmmm... indeed it's clearly not a very helpful message since it even
misled its original author.  I think when I wrote it I assumed it would
only occur because of an internal bug, but clearly it can occur in
other cases.

I'm not sure what would be a good error message.
Maybe something like "`cl-progv` defined too late"?


        Stefan