The comparison of two vectors should return a signed result. hasIntegerRepresentation...

The comparison of two vectors should return a signed result. hasIntegerRepresentation() used to always return false for vectors, but since it was changed, it also
changed the return type of a compare of two unsigned vectors to be unsigned. This patch removes the check for hasIntegerRepresentation since its not needed and returns the appropriate signed type.
I added a new test case and updated exisiting test cases that assumed an unsigned result.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@142250 91177308-0d34-0410-b5e6-96231b3b80d8