now that NEW_STRING_APIS is turned on in the actual string headers, I needed to move some defs around. Also setting a new define for HAVE_CPP_2BYTE_WCHAR_T

xpcom/tests/StringFactoringTests/StringTestProfileOld.Prefix

@@ -1,4 +1,6 @@
 // StringTestProfileOld.Prefix
 
 #include "StringTest.Prefix"
-#undef NEW_STRING_APIS
+
+#define OLD_STRING_APIS
+#undef HAVE_CPP_2BYTE_WCHAR_T

xpcom/tests/StringFactoringTests/StringTestProfileStd.Prefix

@@ -1,5 +1,7 @@
 // StringTestProfileOld.Prefix
 
 #include "StringTest.Prefix"
-#undef NEW_STRING_APIS
+
+#define OLD_STRING_APIS
 #define TEST_STD_STRING
+#undef HAVE_CPP_2BYTE_WCHAR_T