[NFC] Add two tests for C++ modules

One test for checking the decls in language linkage shouldn't be
discarded and can be mangled correctly.

Another one for checking we can't export again in an export decl.

diff --git a/clang/test/Modules/export-in-another-export.cppm b/clang/test/Modules/export-in-another-export.cppm
new file mode 100644 (file)
index 0000000..38cb4d6
--- /dev/null
+++ b/clang/test/Modules/export-in-another-export.cppm
@@ -0,0 +1,5 @@
+// RUN: %clang_cc1 -std=c++20 %s -fsyntax-only -verify
+export module M;
+export { // expected-note {{export block begins here}}
+    export int foo() { return 43; } // expected-error {{export declaration appears within another export declaration}}
+}

diff --git a/clang/test/Modules/language-linkage.cppm b/clang/test/Modules/language-linkage.cppm
new file mode 100644 (file)
index 0000000..bf7982c
--- /dev/null
+++ b/clang/test/Modules/language-linkage.cppm
@@ -0,0 +1,18 @@
+// Make sure that the declarations inside the language linkage can
+// be generated correctly.
+//
+// RUN: rm -fr %t
+// RUN: mkdir %t
+//
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %s -emit-module-interface -o %t/M.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/M.pcm -S -emit-llvm -disable-llvm-passes -o - | FileCheck %s
+export module M;
+
+extern "C++" {
+void foo() {} 
+}
+
+extern "C" void bar() {}
+
+// CHECK: define {{.*}}@bar(
+// CHECK: define {{.*}}@_Z3foov(