cranelift: Remove of/nof overflow flags from icmp (#4879)

* cranelift: Remove of/nof overflow flags from icmp

Neither Wasmtime nor cg-clif use these flags under any circumstances.
From discussion on #3060 I see it's long been unclear what purpose these
flags served.

Fixes #3060, fixes #4406, and fixes #4875... by deleting all the code
that could have been buggy.

This changes the cranelift-fuzzgen input format by removing some IntCC
options, so I've gone ahead and enabled I128 icmp tests at the same
time. Since only the of/nof cases were failing before, I expect these to
work.

* Restore trapif tests

It's still useful to validate that iadd_ifcout's iflags result can be
forwarded correctly to trapif, and for that purpose it doesn't really
matter what condition code is checked.

cranelift/codegen/src/isa/s390x/inst/args.rs

@@ -233,8 +233,6 @@ impl Cond {
             IntCC::UnsignedGreaterThan => 2,
             IntCC::UnsignedLessThanOrEqual => 8 | 4,
             IntCC::UnsignedLessThan => 4,
-            IntCC::Overflow => 1,
-            IntCC::NotOverflow => 8 | 4 | 2,
         };
         Cond { mask }
     }

cranelift/codegen/src/isa/s390x/lower/isle.rs

@@ -891,7 +891,5 @@ fn condcode_is_signed(cc: IntCC) -> bool {
         IntCC::UnsignedGreaterThan => false,
         IntCC::UnsignedLessThanOrEqual => false,
         IntCC::UnsignedLessThan => false,
-        IntCC::Overflow => true,
-        IntCC::NotOverflow => true,
     }
 }