Fix determinism of compiled modules (#3229)

* Fix determinism of compiled modules

Currently wasmtime's compilation artifacts are not deterministic due to
the usage of `HashMap` during serialization which has randomized order
of its elements. This commit fixes that by switching to a sorted
`BTreeMap` for various maps. A test is also added to ensure determinism.

If in the future the performance of `BTreeMap` is not as good as
`HashMap` for some of these cases we can implement a fancier
`serialize_with`-style solution where we sort keys during serialization,
but only during serialization and otherwise use a `HashMap`.

* fix lightbeam

crates/cranelift/src/compiler.rs

@@ -20,7 +20,7 @@ use cranelift_wasm::{
 };
 use std::any::Any;
 use std::cmp;
-use std::collections::{BTreeSet, HashMap};
+use std::collections::{BTreeMap, BTreeSet};
 use std::convert::TryFrom;
 use std::mem;
 use std::sync::Mutex;
@@ -306,7 +306,7 @@ impl wasmtime_environ::Compiler for Compiler {
         self.isa.triple()
     }
 
-    fn flags(&self) -> HashMap<String, FlagValue> {
+    fn flags(&self) -> BTreeMap<String, FlagValue> {
         self.isa
             .flags()
             .iter()
@@ -314,7 +314,7 @@ impl wasmtime_environ::Compiler for Compiler {
             .collect()
     }
 
-    fn isa_flags(&self) -> HashMap<String, FlagValue> {
+    fn isa_flags(&self) -> BTreeMap<String, FlagValue> {
         self.isa
             .isa_flags()
             .iter()