On AIX 4.3.3, building branch-1-5 fails because configure selects
-qlanglvl=extc89, but that in turn causes __STDC__ not to be defined
(unlike without -qlanglvl=extc89, or with -qlanglvl=stdc89 instead).
And of course the build then fails because /**/ isn't recognized as
string concatenator.
I tested building branch-1-5 with CVS Autoconf, which causes the flag
to be selected, but I think Autoconf-2.61 does that as well. (Not sure
whether this can be considered an Autoconf bug.)
Anyway, I'm not totally sure whether the patch below is the right thing
to do. But since `defined (__STDC__) || defined (_AIX)' is used in a
number of places in ltdl.h, I guess it's good enough, so I applied it.
I'd appreciate comments though.