C extension:

Recent manuals say:

The G++ minimum and maximum operators (‘<?’ and ‘>?’) and their compound forms (‘<?=’) and ‘>?=’) have been deprecated and are now removed from G++. Code using these operators should be modified to use std::min and std::max instead.

A quick search of the past documents seems to indicate that they were removed around version 4.0 (3.4.6 includes them, 4.0.4 does not).