wasm2js: coerce function pointer indexes (#2979)

We emit FUNCTION_TABLE[ptr], where FUNCTION_TABLE is a JS
array. That is a rare case where true is handled differently than 1
(a typed array or an add would cast, etc.), so we must explicitly cast
there.

Fixes an issue that existed before, but became a problem due to
#2869 which optimized some selects into a form that emitted a true
or a false, and if that was a function pointer, it could be bad, see

https://app.circleci.com/pipelines/github/emscripten-core/emscripten/6699/workflows/0c4da49c-75d0-4b0a-8fac-686a8330a3fe/jobs/336520

The new test/wasm2js/indirect-select.2asm.js.opt output shows
what happened there.

Verified as passing emscripten's wasm2js1 wasm2js2 test suites.

1 files changed, 1 insertions, 1 deletions

diff --git a/test/wasm2js/func-ptr-offset.2asm.js.opt b/test/wasm2js/func-ptr-offset.2asm.js.opt
index 1c2457fc9..b1198607d 100644
--- a/test/wasm2js/func-ptr-offset.2asm.js.opt
+++ b/test/wasm2js/func-ptr-offset.2asm.js.opt
@@ -34,7 +34,7 @@ function asmFunc(global, env, buffer) {
  
  function $3($0) {
   $0 = $0 | 0;
-  return FUNCTION_TABLE[$0]() | 0;
+  return FUNCTION_TABLE[$0 | 0]() | 0;
  }
  
  var FUNCTION_TABLE = [null, t1, t2, t3];