Add #! line to top of JS file

Previously we could only add this when we detect that we running under
autoconf.

With this change we now default to outputting a JS file that is
executable unless as long as we are possibly targetting node
(ENVIRONMENT_MAY_BE_NODE) and we are not optimizing for size (`-Oz` or
`-Os`).

Also, conditionally add `--experimental-wasm-threads` to the node
command (similar to what we did in #15590) used in the #! line.

Author: sbc100

ChangeLog.md

@@ -159,6 +159,10 @@ See docs/process.md for more on how version tagging works.
   processed as the last item after all system provided JS libraries have been
   added to the build. This fix enables overriding WebGL 2 symbols from user JS
   libraries.
+- The JavaScript file output by emscripten is now marked as executable and
+  given a `#!` line to run under node, as long as node is a possible
+  `ENVIRONMENT` and `-Oz` or `-Os` is not used (since this adds a few bytes
+  to the resulting JavaScript file).
 
 3.0.0 - 11/22/2021
 ------------------

emcc.py

@@ -605,6 +605,8 @@ def check_human_readable_list(items):
 def make_js_executable(script):
   src = read_file(script)
   cmd = shared.shlex_join(config.JS_ENGINE)
+  if settings.USE_PTHREADS:
+    cmd += ' --experimental-wasm-threads'
   if not os.path.isabs(config.JS_ENGINE[0]):
     # TODO: use whereis etc. And how about non-*NIX?
     cmd = '/usr/bin/env -S ' + cmd
@@ -1567,6 +1569,12 @@ def phase_linker_setup(options, state, newargs, user_settings):
     # Add `#!` line to output JS and make it executable.
     options.executable = True
 
+  if settings.ENVIRONMENT_MAY_BE_NODE and not settings.SHRINK_LEVEL:
+    # Older browsers don't support ignoring the #! line
+    # https://github.com/tc39/proposal-hashbang
+    if settings.MIN_CHROME_VERSION < 74 or settings.MIN_FIREFOX_VERSION < 67 or settings.MIN_IE_VERSION != 0x7fffffff:
+      options.executable = True
+
   ldflags = emsdk_ldflags(newargs)
   for f in ldflags:
     add_link_flag(state, sys.maxsize, f)

tests/common.py

@@ -589,7 +589,7 @@ def verify_es5(self, filename):
       #  ES-Check: there were no ES version matching errors!
       # pipe stdout and stderr so that we can choose if/when to print this
       # output and avoid spamming stdout when tests are successful.
-      shared.run_process(es_check + ['es5', os.path.abspath(filename)], stdout=PIPE, stderr=STDOUT, env=es_check_env)
+      shared.run_process(es_check + ['es5', os.path.abspath(filename), '--allow-hash-bang'], stdout=PIPE, stderr=STDOUT, env=es_check_env)
     except subprocess.CalledProcessError as e:
       print(e.stdout)
       self.fail('es-check failed to verify ES5 output compliance')