[HACKERS] Q: How to #ifdef for dlopen() or a specific OS Version

[Zeugswetter Andreas SB]

For a patch to fix the AIX port I would like to differentiate
Versions below 4.3 and above, or rather I would like to 
differentiate whether -ldl has dlopen().

A compiler define would be _AIX43, but I guess we are supposed to 
use a define from configure.

Thanks
Andreas