[regexp] Fix passing all flags to RegExp construction

test/mjsunit/harmony/regexp-dotall.js

Index: test/mjsunit/harmony/regexp-dotall.js
diff --git a/test/mjsunit/harmony/regexp-dotall.js b/test/mjsunit/harmony/regexp-dotall.js
index 9bf78431a9dca19fc0f4bdb34dff48193c731a00..eed5d26f05d2e1687f80831fc1253612eec0ad2b 100644
--- a/test/mjsunit/harmony/regexp-dotall.js
+++ b/test/mjsunit/harmony/regexp-dotall.js
@@ -56,6 +56,12 @@ function toSlowMode(re) {
   assertFalse(re.dotAll);
 }
 
+// Different construction variants with all flags.
+{
+  assertEquals("gimsuy", new RegExp("", "yusmig").flags);
+  assertEquals("gimsuy", new RegExp().compile("", "yusmig").flags);
+}
+
 // Default '.' behavior.
 {
   let re = /^.$/;