[NFC][InstCombine] Add xor-or-icmp tests with icmp having extra uses

Currently InstCombiner::foldXorOfICmps() bailouts if the
ICMP it wants to invert has extra uses. As it can be seen
in the tests in previous commit, this is super unfortunate,
this is the single pattern that is left non-canonicalized.

We could analyze if we can also invert all the uses if said ICMP
at the same time, thus not bailing out there.
I'm not seeing any nicer alternative.

llvm-svn: 367439