Patch installed for warning in concat.c

[DJ Delorie]

> Autoconf has started recommending the use of `#if', so that if you
> define HAVE_STDLIB_H to 0 (which is a perfectly reasonable thing to
> do, if you ask me), you still get the right result.  Also, if you fail
> to test for stdlib.h, the absence of a #define HAVE_STDLIB_H will make
> #if and #ifdef equivalent.

But what about older compilers that barf with a #if with an undefined
symbol?