Revert "Respect integer overflow handling in abs builtin"

This reverts commit 17831857,
which broke the buildbots, starting with when it was first built in https://lab.llvm.org/buildbot/#/builders/85/builds/18390

(N.B. I think the patch is uncovering real bugs; the revert
is simply to keep the tree green and the buildbots useful, because I'm not confident how to
fix-forward all the found bugs.)