[X86] Add some more movmsk test cases. NFC

These IR patterns represent the exact behavior of a movmsk instruction using (zext (bitcast (icmp slt X, 0))).

For the v4i32/v8i32/v2i64/v4i64 we currently emit a PCMPGT for the icmp slt which is unnecessary since we only care about the sign bit of the result. This is because of the int->fp bitcast we put on the input to the movmsk nodes for these cases. I'll be fixing this in a future patch.

llvm-svn: 343045