[javascript] Support TI_EMSCRIPTENED option as an env var (JS 3/n) (#…

…4106)

setup.py

@@ -136,6 +136,10 @@ def run(self):
             f'-DTI_VERSION_PATCH={TI_VERSION_PATCH}',
         ]
 
+        emscriptened = os.getenv('TI_EMSCRIPTENED', '0') in ('1', 'ON')
+        if emscriptened:
+            cmake_args += ['-DTI_EMSCRIPTENED=ON']
+
         if shutil.which('ninja'):
             cmake_args += ['-GNinja']