Re: fix tar bootstrap

[Eric Blake]

Bruno asked:
> So, the general rule is: If a macro FOO is defined through m4_define or
> m4_pushdef, then to get its value *without further evaluations or 
> interpretation*
> one needs to write
> 
>       ...]m4_defn([FOO])[...
> 
> not
> 
>       ...]FOO[...
> 
> Is that right?

Yes.  Or put another way, m4_defn is the only safe way to
retrieve the contents of a macro used to store arbitrary text.  You
can optimize and use macro invocation if you are sure that
the macro's contents will not contain $, quotes, comments,
or further macro names (as is the case with the neighboring
usage of gl_LIBSOURCES_LIST, since we control the file
names that get committed into gnulib.git).

And even then, if you have m4_changequote currently set to
anything other than the normal [], then m4_defn might still
suffer from interpolation of the macro's definition according
to the changed quoting rules (yet another reason why the
autoconf manual discourages the use of m4_changequote).

-- 
Eric Blake