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/frontend/src/frontend.rs

@@ -1005,7 +1005,7 @@ impl<'a> FunctionBuilder<'a> {
     /// misbehave as described in [`MemFlags::aligned`].
     ///
     /// Note that `memcmp` is a *big-endian* and *unsigned* comparison.
-    /// As such, this panics when called with `IntCC::Signed*` or `IntCC::*Overflow`.
+    /// As such, this panics when called with `IntCC::Signed*`.
     pub fn emit_small_memory_compare(
         &mut self,
         config: TargetFrontendConfig,
@@ -1034,9 +1034,6 @@ impl<'a> FunctionBuilder<'a> {
             | SignedLessThanOrEqual => {
                 panic!("Signed comparison {} not supported by memcmp", int_cc)
             }
-            Overflow | NotOverflow => {
-                panic!("Overflow comparison {} not supported by memcmp", int_cc)
-            }
         };
 
         if size == 0 {