[Gc] Avoid ABORT() in GC_log_printf

[Kjetil Matheussen]

Hi,

I just got a crash which I think was caused by running my program in a 
read-only directory.

WRITE failed in GC_log_printf, and then ABORT() was called.

Perhaps there is a configuration flag I can set which prevents ABORT 
from aborting?
(didn't find any though). I don't want the garbage collector to abort 
the program
in production code, even if it could be a serious error.

I'll just redefine ABORT for now, but I think the default behavior 
needs to be changed.
(It could of course also be that I have misunderstood something)

-Kjetil