CPlusPlus: Add parser support for declarations of user-defined literals

... without a space before the identifier.

Change-Id: I977ffae82eb86f5ae6ea594cba17cc486e63bf6c
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

tests/auto/cplusplus/cxx11/data/userDefinedLiterals.2.cpp

@@ -0,0 +1,7 @@
+wchar_t operator ""_wc(const wchar_t c) { return c; }
+
+int main()
+{
+    const auto c = L'c'_wc;
+    return c;
+}