Define timing_selftest() even with TIMING_ALT
diff --git a/include/mbedtls/timing.h b/include/mbedtls/timing.h
index 5ad4f9e..0ef1827 100644
--- a/include/mbedtls/timing.h
+++ b/include/mbedtls/timing.h
@@ -79,6 +79,18 @@
  */
 void mbedtls_timing_m_sleep( int milliseconds );
 
+#ifdef __cplusplus
+}
+#endif
+
+#else  /* MBEDTLS_TIMING_ALT */
+#include "timing_alt.h"
+#endif /* MBEDTLS_TIMING_ALT */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #if defined(MBEDTLS_SELF_TEST)
 /**
  * \brief          Checkup routine
@@ -92,8 +104,4 @@
 }
 #endif
 
-#else  /* MBEDTLS_TIMING_ALT */
-#include "timing_alt.h"
-#endif /* MBEDTLS_TIMING_ALT */
-
 #endif /* timing.h */