CMSIS-DSP: Update header for use from C++

Platforms/IPSS/ipss_bench.h

@@ -1,7 +1,16 @@
 #ifndef IPSS_BENCH_H
 #define IPSS_BENCH_H 
 
-extern void start_ipss_measurement();
+#ifdef   __cplusplus
-extern void stop_ipss_measurement();
+extern "C"
+{
+#endif
+
+void start_ipss_measurement();
+void stop_ipss_measurement();
+
+#ifdef   __cplusplus
+}
+#endif
 
 #endif