newfangled sh in libtool

[Karl Berry]

In the func_arith function in libtool 2.2.6, the "newfangled" $(( ... ))
sh construct is used.  In particular, Solaris 5.10 /bin/sh does not
recognize it:
./libtool: syntax error at line 653: `func_arith_result=$' unexpected

I'm not sure if this is the only place where such a thing is used, but
it's the only one I've run across.  It's rather a drag, since it means
every libtool-using package has to check for a "new" sh, even if the
package itself doesn't need it.

If this really is the only place, how about using expr instead?

(Sorry if this is a well-known topic.)

Best,
karl