[NFC] [C++20] [Modules] Add tests for template instantiation in transitive imported module

[ChuanqiXu]

Summary

This patch adds two test about template class instantiation in transitively imported module. They are used as pre-commit tests for successive patches.

The original commit fail in windows. It is odd since I think this should be target-independent. I don't have window environment so I sent this to test it.

[ChuanqiXu]

Update command line

[ChuanqiXu]

Now the windows tests passed, this should be good.

clang/test/Modules/Inputs/module-transtive-instantiation/Templ.cppm

+export module Templ;
+export template <class T>
+class G {
+public:
+    T operator()() {
+        return T();
+    }
+};

clang/test/Modules/Inputs/module-transtive-instantiation/bar.cppm

+export module bar;
+import Templ;
+export template<class T>
+int bar() {
+    return G<T>()();
+}

clang/test/Modules/module-transtive-instantiation-2.cpp

+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: %clang_cc1 -std=c++20 %S/Inputs/module-transtive-instantiation/Templ.cppm -emit-module-interface -o %t/Templ.pcm
+// RUN: %clang_cc1 -std=c++20 %S/Inputs/module-transtive-instantiation/bar.cppm  -emit-module-interface -fprebuilt-module-path=%t -o %t/bar.pcm
+// RUN: %clang_cc1 -std=c++20 -fprebuilt-module-path=%t %s -fsyntax-only -verify
+
+import bar;
+int foo() {
+    G<int> g;    // expected-error {{declaration of 'G' must be imported from module 'Templ' before it is required}}
+    return g();  // expected-note@Inputs/module-transtive-instantiation/Templ.cppm:3 {{declaration here is not visible}}
+}

clang/test/Modules/module-transtive-instantiation.cpp

+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: %clang_cc1 -std=c++20 %S/Inputs/module-transtive-instantiation/Templ.cppm -emit-module-interface -o %t/Templ.pcm
+// RUN: %clang_cc1 -std=c++20 %S/Inputs/module-transtive-instantiation/bar.cppm  -emit-module-interface -fprebuilt-module-path=%t -o %t/bar.pcm
+// RUN: %clang_cc1 -std=c++20 -fprebuilt-module-path=%t %s -fsyntax-only -verify
+
+import bar;
+int foo() {
+    // FIXME: It shouldn't be an error. Since the `G` is already imported in bar.
+    return bar<int>(); // expected-error@Inputs/module-transtive-instantiation/bar.cppm:5 {{definition of 'G' must be imported from module 'Templ' before it is required}}
+                       // expected-note@-1 {{in instantiation of function template specialization 'bar<int>' requested here}}
+                       // expected-note@Inputs/module-transtive-instantiation/Templ.cppm:3 {{definition here is not reachable}}
+}