binaryen.js: use ECMASCRIPT6 for Closure Compiler (#2990)

Author: MaxGraey

CMakeLists.txt

@@ -352,6 +352,7 @@ if(EMSCRIPTEN)
   target_link_libraries(binaryen_wasm "--extern-pre-js ${CMAKE_CURRENT_SOURCE_DIR}/src/js/binaryen.js-extern-pre.js")
   target_link_libraries(binaryen_wasm "--extern-post-js ${CMAKE_CURRENT_SOURCE_DIR}/src/js/binaryen.js-extern-post.js")
   target_link_libraries(binaryen_wasm optimized "--closure 1")
+  target_link_libraries(binaryen_wasm optimized "--closure-args \"--language_in=ECMASCRIPT6 --language_out=ECMASCRIPT6\"")
   target_link_libraries(binaryen_wasm optimized "--llvm-lto 1")
   target_link_libraries(binaryen_wasm debug "--profiling")
   set_property(TARGET binaryen_wasm PROPERTY CXX_STANDARD 14)
@@ -366,7 +367,7 @@ if(EMSCRIPTEN)
   target_link_libraries(binaryen_js "-s WASM_ASYNC_COMPILATION=0")
   if(${CMAKE_CXX_COMPILER_VERSION} STREQUAL "6.0.1")
     # only valid with fastcomp and WASM=0
-    target_link_libraries(binaryen_js "-s ELIMINATE_DUPLICATE_FUNCTIONS=1")	
+    target_link_libraries(binaryen_js "-s ELIMINATE_DUPLICATE_FUNCTIONS=1")
   endif()
   target_link_libraries(binaryen_js "-s NO_FILESYSTEM=0")
   target_link_libraries(binaryen_js "-s NODERAWFS=0")
@@ -375,6 +376,7 @@ if(EMSCRIPTEN)
   target_link_libraries(binaryen_js "--extern-pre-js ${CMAKE_CURRENT_SOURCE_DIR}/src/js/binaryen.js-extern-pre.js")
   target_link_libraries(binaryen_js "--extern-post-js ${CMAKE_CURRENT_SOURCE_DIR}/src/js/binaryen.js-extern-post.js")
   target_link_libraries(binaryen_js optimized "--closure 1")
+  target_link_libraries(binaryen_js optimized "--closure-args \"--language_in=ECMASCRIPT6 --language_out=ECMASCRIPT6\"")
   target_link_libraries(binaryen_js optimized "--llvm-lto 1")
   target_link_libraries(binaryen_js debug "--profiling")
   target_link_libraries(binaryen_js debug "-s ASSERTIONS")