#ifdef wrap the _rs_forkhandler
do not need a variable to track locking, since all code paths have it
locked throughout.
Only call getauxval(3) if HAVE_GETAUXVAL is defined.  Fixes build on older
Linux (such as Ubuntu 12.04LTS) that don't have it yet.  Seems the AT_XXX
defines are pulled in by <link.h> now.

ok beck@