Comment 92 for bug 727064

No (except for LD_PRELOAD).
The thing is, the IFUNC decision function can be only very limited, it is called during relocation processing, so it can't rely too much on relocation processing having been performed already. And it must be very fast and thread-safe, doing getenv there would be very problematic. It usually just either tests cpuid flags or tests saved cpuid flags and vars computed from that.
Plus, each of the function usually has a different set of decisions, there is no common notion of oldest etc.