Make try body start with 'do' (#2846)

In WebAssembly/exception-handling#52, We decided to put `try` bodies in
a `do` clause to be more consistent with `catch`.

- Before
```wast
(try
  ...
  (catch
    ...
  )
)
```

- After
```wast
(try
  (do
    ...
  )
  (catch
    ...
  )
)
```

Another upside of this change is when there are multiple instructions
within a `try` body, we no longer need to wrap them in a `block`.

1 files changed, 3 insertions, 1 deletions

diff --git a/test/passes/generate-stack-ir_optimize-stack-ir_print-stack-ir_all-features.wast b/test/passes/generate-stack-ir_optimize-stack-ir_print-stack-ir_all-features.wast
index c355a2bf1..6a53b2283 100644
--- a/test/passes/generate-stack-ir_optimize-stack-ir_print-stack-ir_all-features.wast
+++ b/test/passes/generate-stack-ir_optimize-stack-ir_print-stack-ir_all-features.wast
@@ -3,7 +3,9 @@
 
   (func $eh (local $exn exnref)
     (try
-      (throw $e0 (i32.const 0))
+      (do
+        (throw $e0 (i32.const 0))
+      )
       (catch
         (local.set $exn (exnref.pop))
         (drop