Support parsing async modifiers for functions. (#3460)

Only parsing is implemented, so the async functions currently behave
like normal function except they return with a resolved Promise object
when the function is terminated correctly.

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

jerry-core/vm/opcodes.c

@@ -26,6 +26,7 @@
 #include "ecma-iterator-object.h"
 #include "ecma-lex-env.h"
 #include "ecma-objects.h"
+#include "ecma-promise-object.h"
 #include "ecma-try-catch-macro.h"
 #include "jcontext.h"
 #include "opcodes.h"
@@ -706,6 +707,21 @@ opfunc_resume_executable_object (vm_executable_object_t *executable_object_p, /*
   return result;
 } /* opfunc_resume_executable_object */
 
+/**
+ * Create a Promise object if needed and resolve it with a value
+ *
+ * @return Promise object
+ */
+ecma_value_t
+opfunc_return_promise (ecma_value_t value) /**< value */
+{
+  ecma_value_t promise = ecma_make_object_value (ecma_builtin_get (ECMA_BUILTIN_ID_PROMISE));
+  ecma_value_t result = ecma_promise_reject_or_resolve (promise, value, true);
+
+  ecma_free_value (value);
+  return result;
+} /* opfunc_return_promise */
+
 #endif /* ENABLED (JERRY_ES2015) */
 
 /**