isle: expand enums in ISLE (#3586)

* x64: expand FloatCC enum in ISLE
* isle: regenerate manifests
* isle: generate all enum fields in `clif.isle`

This expands the `gen_isle` function to write all of the immediate
`enum`s out explicitly in `clif.isle`. Non-`enum` immediates are still
`extern primitive`.

* Only compile `enum_values` with `rebuild-isle` feature
* Only compile `gen_enum_isle` with `rebuild-isle` feature

cranelift/codegen/meta/src/cdsl/operands.rs

@@ -111,6 +111,17 @@ pub(crate) enum OperandKindFields {
     TypeVar(TypeVar),
 }
 
+impl OperandKindFields {
+    /// Return the [EnumValues] for this field if it is an `enum`.
+    #[cfg(feature = "rebuild-isle")]
+    pub(crate) fn enum_values(&self) -> Option<&EnumValues> {
+        match self {
+            OperandKindFields::ImmEnum(map) => Some(map),
+            _ => None,
+        }
+    }
+}
+
 #[derive(Clone, Debug)]
 pub(crate) struct OperandKind {
     /// String representation of the Rust type mapping to this OperandKind.