[strong] Disallow implicit conversions for add

src/builtins.h

Index: src/builtins.h
diff --git a/src/builtins.h b/src/builtins.h
index 79d6f61c2c0fbb84b13b33042b3f746a51be5977..fdeae5506347372773941fbc5577af2d3acf5496 100644
--- a/src/builtins.h
+++ b/src/builtins.h
@@ -170,6 +170,7 @@ enum BuiltinExtraArguments {
   V(STRICT_EQUALS, 1)                      \
   V(COMPARE, 2)                            \
   V(ADD, 1)                                \
+  V(ADD_STRONG, 1)                         \
   V(SUB, 1)                                \
   V(SUB_STRONG, 1)                         \
   V(MUL, 1)                                \
@@ -203,7 +204,9 @@ enum BuiltinExtraArguments {
   V(TO_STRING, 0)                          \
   V(TO_NAME, 0)                            \
   V(STRING_ADD_LEFT, 1)                    \
+  V(STRING_ADD_LEFT_STRONG, 1)             \
   V(STRING_ADD_RIGHT, 1)                   \
+  V(STRING_ADD_RIGHT_STRONG, 1)            \
   V(APPLY_PREPARE, 1)                      \
   V(REFLECT_APPLY_PREPARE, 1)              \
   V(REFLECT_CONSTRUCT_PREPARE, 2)          \