wasm-reduce: Enable GlobalTypeOptimization (#7887)

We made that pass require --closed-world at some point. Since then, all
attempts by the reducer to use it failed, sadly.

This helps reduce some GC testcases quite a lot.

Author: kripken

src/tools/wasm-reduce/wasm-reduce.cpp

@@ -279,7 +279,7 @@ struct Reducer
       "--dce",
       "--duplicate-function-elimination",
       "--enclose-world",
-      "--gto",
+      "--gto --closed-world",
       "--inlining",
       "--inlining-optimizing",
       "--optimize-level=3 --inlining-optimizing",

test/reduce/gc.wast

@@ -1,5 +1,6 @@
 (module
   (rec
+    ;; The funcref field can be optimized away with --gto.
     (type $A (struct (field (mut i32)) (field funcref)))
     ;; This type can be optimized away.
     (type $unused (struct))

test/reduce/gc.wast.txt

@@ -1,5 +1,5 @@
 (module
- (type $0 (struct (field (mut i32)) (field funcref)))
+ (type $0 (struct (field (mut i32))))
  (type $1 (func (result i32)))
  (global $global$0 (ref null $0) (struct.new_default $0))
  (export "use-global" (func $0))