Make CanXFormVExtractWithShuffleIntoLoad reject loads with multiple uses. Also...

Make CanXFormVExtractWithShuffleIntoLoad reject loads with multiple uses. Also make it return false if there's not even a load at all. This makes the code better match the code in DAGCombiner that it tries to match. These two changes prevent some cases where vector_shuffles were making it to instruction selection and causing the older shuffle selection code to be triggered. Also needed to fix a bad pattern that this change exposed. This is the first step towards getting rid of the old shuffle selection support. No test cases yet because there's no way to tell whether a shuffle was handled in the legalize stage or at instruction selection.

llvm-svn: 147428