[clang-repl] Additional test for disambiguation of templates

This test case was fixed in commit 2c4620c ("Consider the scope spec
in template lookups for deduction guides."), but it is worth having a
dedicated test case with a templated struct and a using declaration.

Differential Revision: https://reviews.llvm.org/D157477

clang/test/Interpreter/disambiguate-decl-stmt.cpp

@@ -11,6 +11,10 @@ extern "C" int printf(const char*,...);
 namespace ns1 { template<typename T> void tmplt(T &) {}}
 int arg_tmplt = 12; ns1::tmplt(arg_tmplt);
 
+namespace ns2 { template <typename T> struct S {}; }
+namespace ns3 { struct A { public: using S = int; }; }
+namespace ns3 { A::S f(A::S a); }
+
 // ParseStatementOrDeclaration returns multiple statements.
 #ifdef MS
 int g_bFlag = 1;