[codegen] add intcc conditions for reading overflow flag

Add conditions to IntCC for checking the overflow flag (Overflow,
NotOverflow).

cranelift/codegen/meta/src/shared/immediates.rs

@@ -129,6 +129,8 @@ impl Immediates {
                 intcc_values.insert("ugt", "UnsignedGreaterThan");
                 intcc_values.insert("ule", "UnsignedLessThanOrEqual");
                 intcc_values.insert("ult", "UnsignedLessThan");
+                intcc_values.insert("of", "Overflow");
+                intcc_values.insert("nof", "NotOverflow");
                 Builder::new_enum("intcc", intcc_values)
                     .doc("An integer comparison condition code.")
                     .default_member("cond")

cranelift/codegen/meta/src/shared/instructions.rs

@@ -1587,6 +1587,7 @@ pub(crate) fn define(
     let y = &operand("y", Int);
 
     // TODO(ryzokuken): Add documentation for unsigned overflow.
+    // TODO(ryzokuken): Add documentation for signed overflow.
     ig.push(
         Inst::new(
             "icmp",