mark P2115 as implemented and add test

Author: kish1n

clang/test/SemaCXX/P2115.cpp

@@ -0,0 +1,21 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+
+// RUN: %clang -std=c++20 -fmodule-header %t/A.h -o %t/A.pcm
+// RUN: %clang -std=c++20 -fmodule-header %t/B.h -o %t/B.pcm
+// RUN: %clang -std=c++20 -fsyntax-only -fmodule-file=%t/A.pcm -fmodule-file=%t/B.pcm %t/main.cpp
+
+//--- A.h
+// expected-no-diagnostics
+enum { A = 0 };
+
+//--- B.h
+// expected-no-diagnostics
+enum { B = 1 };
+
+//--- main.cpp
+// expected-no-diagnostics
+import "A.h";
+import "B.h";
+int main() {}