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/preprocessor/headers/foo.h b/tools/versioner/tests/preprocessor/headers/foo.h
index 81c8b4b..2429334 100644
--- a/tools/versioner/tests/preprocessor/headers/foo.h
+++ b/tools/versioner/tests/preprocessor/headers/foo.h
@@ -1,3 +1,7 @@
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
 int always_available();
 
 int also_always_available() __INTRODUCED_IN(9);
@@ -42,3 +46,7 @@
 int group_lp32() __INTRODUCED_IN_ARM(12) __INTRODUCED_IN_X86(12) __INTRODUCED_IN_MIPS(12);
 
 int future() __INTRODUCED_IN_FUTURE;
+
+#if defined(__cplusplus)
+}
+#endif