[X86] Add test cases that show the current codegen for (trunc (srl (mul ext, ext), 16)). NFC

A future patch will turn this into MULHU/MULHS.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330519 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed