Remove IFLAGS/FFLAGS types (#5406)

All instructions using the CPU flags types (IFLAGS/FFLAGS) were already
removed.  This patch completes the cleanup by removing all remaining
instructions that define values of CPU flags types, as well as the
types themselves.

Specifically, the following features are removed:
- The IFLAGS and FFLAGS types and the SpecialType category.
- Special handling of IFLAGS and FFLAGS in machinst/isle.rs and
  machinst/lower.rs.
- The ifcmp, ifcmp_imm, ffcmp, iadd_ifcin, iadd_ifcout, iadd_ifcarry,
  isub_ifbin, isub_ifbout, and isub_ifborrow instructions.
- The writes_cpu_flags instruction property.
- The flags verifier pass.
- Flags handling in the interpreter.

All of these features are currently unused; no functional change
intended by this patch.

This addresses https://github.com/bytecodealliance/wasmtime/issues/3249.

cranelift/codegen/src/verifier/mod.rs

@@ -57,7 +57,6 @@
 //! - Swizzle and shuffle instructions take a variable number of lane arguments. The number
 //!   of arguments must match the destination type, and the lane indexes must be in range.
 
-use self::flags::verify_flags;
 use crate::dbg::DisplayList;
 use crate::dominator_tree::DominatorTree;
 use crate::entity::SparseSet;
@@ -81,8 +80,6 @@ use alloc::vec::Vec;
 use core::cmp::Ordering;
 use core::fmt::{self, Display, Formatter};
 
-mod flags;
-
 /// A verifier error.
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub struct VerifierError {
@@ -1799,8 +1796,6 @@ impl<'a> Verifier<'a> {
             self.encodable_as_bb(block, errors)?;
         }
 
-        verify_flags(self.func, &self.expected_cfg, errors)?;
-
         if !errors.is_empty() {
             log::warn!(
                 "Found verifier errors in function:\n{}",