Slaps 50 gallons of cold water on face . . . .
Where to find the information:
Look in the C library ./configuration file - there will be a test for the minimum kernel header version required.
It will be using an m4 macro, but should be easy to spot.
The minimum version was bumped to 2.6.20.x over time for some feature(s) - I don't recall what, or if we need those features.
(I will not swear to that, haven't had my head in the building of the C library for a long time.)