versioner: add extern "C" to tests.

Bug: https://github.com/android-ndk/ndk/issues/440
Test: python run_tests.py
Change-Id: Id893979146bc609a17bd1fa2a6bec6f10dfe4804
diff --git a/tools/versioner/tests/multiple_definition/headers/foo.h b/tools/versioner/tests/multiple_definition/headers/foo.h
index a9d0197..29592c6 100644
--- a/tools/versioner/tests/multiple_definition/headers/foo.h
+++ b/tools/versioner/tests/multiple_definition/headers/foo.h
@@ -1,3 +1,11 @@
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
 static int foo() {
   return 0;
 }
+
+#if defined(__cplusplus)
+}
+#endif