[InstCombine] Propagate nsw flag when turning mul by pow2 into shift when the...

[InstCombine] Propagate nsw flag when turning mul by pow2 into shift when the constant is a vector splat or the scalar bit width is larger than 64-bits

The check to see if we can propagate the nsw flag used m_ConstantInt(uint64_t*&) which doesn't work with splat vectors and has a restriction that the bitwidth of the ConstantInt must be 64-bits are less.

This patch changes it to use m_APInt to remove both these issues

Differential Revision: https://reviews.llvm.org/D34699

llvm-svn: 306457