Don't assert that linkage decls are always C++, it's not true. Fixes PR5019.

llvm-svn: 82557
diff --git a/clang/test/CodeGenCXX/mangle.cpp b/clang/test/CodeGenCXX/mangle.cpp
index d952f31..dbcd0c9 100644
--- a/clang/test/CodeGenCXX/mangle.cpp
+++ b/clang/test/CodeGenCXX/mangle.cpp
@@ -130,3 +130,10 @@
  void h() { } 
 }
 
+// PR5019
+extern "C" { struct a { int b; }; }
+
+// CHECK: @_Z1fP1a
+int f(struct a *x) {
+    return x->b;
+}