Change how flags are stored in serialized modules.

This commit changes how both the shared flags and ISA flags are stored in the
serialized module to detect incompatibilities when a serialized module is
instantiated.

It improves the error reporting when a compiled module has mismatched shared
flags.

cranelift/codegen/src/isa/x64/mod.rs

@@ -9,7 +9,7 @@ use crate::isa::Builder as IsaBuilder;
 use crate::machinst::{compile, MachBackend, MachCompileResult, TargetIsaAdapter, VCode};
 use crate::result::CodegenResult;
 use crate::settings::{self as shared_settings, Flags};
-use alloc::{borrow::ToOwned, boxed::Box, string::String, vec::Vec};
+use alloc::{boxed::Box, vec::Vec};
 use core::hash::{Hash, Hasher};
 use regalloc::{PrettyPrint, RealRegUniverse, Reg};
 use target_lexicon::Triple;
@@ -85,15 +85,8 @@ impl MachBackend for X64Backend {
         &self.flags
     }
 
-    fn enabled_isa_flags(&self) -> Vec<String> {
-        self.x64_flags
-            .iter_enabled()
-            .map(ToOwned::to_owned)
-            .collect()
-    }
-
-    fn is_flag_enabled(&self, flag: &str) -> bool {
-        self.x64_flags.is_enabled(flag)
+    fn isa_flags(&self) -> Vec<shared_settings::Value> {
+        self.x64_flags.iter().collect()
     }
 
     fn hash_all_flags(&self, mut hasher: &mut dyn Hasher) {