Fix build on Solaris 11.4

[rouault]

No description provided.

[hobu]

This fix seems not worth it. It makes the code more confusing, and do we really need to care about ancient Solaris?

[rouault]

Actually, it matches more the signature of the manpage of dladdr() on Linux too:

       #define _GNU_SOURCE
       #include <dlfcn.h>

       int dladdr(void *addr, Dl_info *info);

[rouault]

But interestingly, on Linux:

$ grep dladdr /usr/include/dlfcn.h 
extern int dladdr (const void *__address, Dl_info *__info)

So it thinks that Linux has 'hardened' things, but POSIX has a looser definition.