[X86] Add more tests for -x86-experimental-vector-widening-legalization

I'm looking into whether we can make this the default legalization strategy. Adding these tests to help cover the changes that will be necessary.

This patch adds copies of some tests with the command line switch enabled. By making copies its easier to compare the two legalization strategies.

I've also removed RUN lines from some of these tests that already had -x86-experimental-vector-widening-legalization

llvm-svn: 346745