This patch enables canonicalization of SPF_ABS and SPF_ABS to the abs intrinsic. This is a recommit, the original try was 05d4c4ebc2fb006b8a2bd05b24c6aba10dd2eef8, but it was reverted due to an apparent miscompile, which since then has just been fixed by the previous commit. Differential Revision: https://reviews.llvm.org/D87188