Don't forego folding of loads into 64-bit adds when the other

Don't forego folding of loads into 64-bit adds when the other
operand is a signed 32-bit immediate. Unlike with the 8-bit
signed immediate case, it isn't actually smaller to fold a
32-bit signed immediate instead of a load. In fact, it's
larger in the case of 32-bit unsigned immediates, because
they can be materialized with movl instead of movq.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@67001 91177308-0d34-0410-b5e6-96231b3b80d8