Patch is self explanatory.
Created attachment 210793 [details, diff]
fixes buggy syntax in configure.ac
Patch applied on behalf of QA and Base System.
Rafał did you send the patch upstream already?
(In reply to comment #2)
> Rafał did you send the patch upstream already?
Well, no. This is another one of the packages,
that I'm not really using and I just came up with this
patch, after I synced today and looked once again
at available lftp packages (I'm mixing stable and unstable
quite a bit, so I had lftp 3.7.15-r1 on my upgrade list for
quite awhile, but was stalling cause I saw 4.0 reaching full release,
today I simply decided to check again and saw 4.0.3 not being masked,
then it failed to emerge, then came the patch).
Amusing, you know.
NEWS of autoconf 2.65 suggests, that with it,
current syntax will work.
lftp is on version 4.0.9 and autoconf is on 2.65 now.