[3.9.1] Merging r280837 [X86] Don't reduce the width of vector mul if the...

[3.9.1] Merging r280837 [X86] Don't reduce the width of vector mul if the target doesn't support SSE2.

The patch is to fix PR30298, which is caused by rL272694. The solution is to
bail out if the target has no SSE2.

Differential Revision: https://reviews.llvm.org/D24288

llvm-svn: 282753