Fix PR6503. This turned into a much more interesting and nasty bug. Various

Fix PR6503.  This turned into a much more interesting and nasty bug.  Various
parts of the cmp|cmp and cmp&cmp folding logic wasn't prepared for vectors
(unrelated to the bug but noticed while in the code) and the code was
*definitely* not safe to use by the (cast icmp)|(cast icmp) handling logic
that I added in r95855.  Fix all this up by changing the various routines
to more consistently use IRBuilder and not pass in the I which had the wrong
type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97801 91177308-0d34-0410-b5e6-96231b3b80d8