Don't set opt_level to best

LICM is still broken

Author: bjorn3

src/lib.rs

@@ -242,7 +242,8 @@ fn build_isa(sess: &Session) -> Box<dyn isa::TargetIsa + 'static> {
         "false"
     }).unwrap();
 
-    flags_builder.set("opt_level", "best").unwrap();
+    // FIXME(CraneStation/cranelift#732) fix LICM in presence of jump tables
+    //flags_builder.set("opt_level", "best").unwrap();
 
     // FIXME enable again when https://github.com/CraneStation/cranelift/issues/664 is fixed
     /*