The strength from Giant corpses has been nerfed in 3.6.0. It's now considered an instrinsic, and therefore given conditionally: For example, fire giants can either give fire resistance or strength now, but not both. There's equal chance of the two benefits being chosen, however even if the giant gives no other instrinsics, strength is always a 50% chance.
The actual amount of strength gained appears to be unchanged.
Line 1068 in eat.c is a comment explaining the new method; the actual code is immediately after. It's largely a part of the 3.4.3 intrinsic code. I'm not linking it since the source code on this wiki is still 3.4.3 -- Qazmlpok (talk) 03:26, 9 December 2015 (UTC)