Emit better error message about writable properties

src/messages.h

Index: src/messages.h
diff --git a/src/messages.h b/src/messages.h
index a47bf57d4527be1f871d4634bba1f3896547b750..12bc86d5cbb3e4c1519099c21a6579d060bbf799 100644
--- a/src/messages.h
+++ b/src/messages.h
@@ -237,8 +237,8 @@ class CallSite {
   T(SimdToNumber, "Cannot convert a SIMD value to a number")                   \
   T(UndefinedOrNullToObject, "Cannot convert undefined or null to object")     \
   T(ValueAndAccessor,                                                          \
-    "Invalid property.  A property cannot both have accessors and be "         \
-    "writable or have a value, %")                                             \
+    "Invalid property descriptor. Cannot both specify accessors and a value "  \
+    "or writable attribute, %")                                                \
   T(VarRedeclaration, "Identifier '%' has already been declared")              \
   T(WithExpression, "% has no properties")                                     \
   T(WrongArgs, "%: Arguments list has wrong type")                             \