Re-apply "[ubsan] Sanity-check shift amounts before truncation"

This re-applies r293343 (reverts commit r293475) with a fix for an
assertion failure caused by a missing integer cast. I tested this patch
by using the built compiler to compile X86FastISel.cpp.o with ubsan.

Original commit message:

Ubsan does not report UB shifts in some cases where the shift exponent
needs to be truncated to match the type of the shift base. We perform a
range check on the truncated shift amount, leading to false negatives.

Fix the issue (PR27271) by performing the range check on the original
shift amount.

Differential Revision: https://reviews.llvm.org/D29234

llvm-svn: 293572