Return "[SCEV] Use context to strengthen flags of BinOps"

This reverts commit 354fa0b4.

Returning as is. The patch was reverted due to a miscompile, but
this patch is not causing it. This patch made it possible to infer
some nuw flags in code guarded by `false` condition, and then someone
else to managed to propagate the flag from dead code outside.

Returning the patch to be able to reproduce the issue.