[X86] Do not lower scalar sdiv/udiv to a shifts + mul sequence when optimizing for minsize

There are some cases where the mul sequence is smaller, but for the most part,
using a div is preferable. This does not apply to vectors, since x86 doesn't
have vector idiv, and a vector mul/shifts sequence ought to be smaller than a
scalarized division.

Differential Revision: http://reviews.llvm.org/D12082

llvm-svn: 245431