[InstCombine] Support vectors in SimplifyAddWithRemainder.

SimplifyAddWithRemainder currently also matches for vector types, but
tries to create an integer constant, which causes a crash.

By using Constant::getIntegerValue() we can support both the scalar and
vector cases.

The 2 added test cases crash without the fix.

Reviewers: spatel, lebedev.ri

Reviewed By: spatel, lebedev.ri

Differential Revision: https://reviews.llvm.org/D75906