[clang-repl][NFC] Fix calling convention mismatch in test

Test failed on x86 platforms due to a calling convention mismatch
when member function was called like a free function. In this patch,
member function is marked static to address this.
diff --git a/clang/unittests/Interpreter/InterpreterTest.cpp b/clang/unittests/Interpreter/InterpreterTest.cpp
index 742aa49..280c6d7f 100644
--- a/clang/unittests/Interpreter/InterpreterTest.cpp
+++ b/clang/unittests/Interpreter/InterpreterTest.cpp
@@ -221,7 +221,7 @@
                                "class A {};"
                                "struct B {"
                                "  template<typename T>"
-                               "  int callme(T) { return 42; }"
+                               "  static int callme(T) { return 42; }"
                                "};"));
   auto &PTU = llvm::cantFail(Interp->Parse("auto _t = &B::callme<A*>;"));
   auto PTUDeclRange = PTU.TUPart->decls();