[components][libc] add extern "C" for header file

components/libc/pthreads/pthread.h

@@ -12,6 +12,11 @@
 #define __PTHREAD_H__
 
 #include <rtthread.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #include <posix_types.h>
 #include <sched.h>
 
@@ -262,4 +267,8 @@ int pthread_barrier_init(pthread_barrier_t           *barrier,
 
 int pthread_barrier_wait(pthread_barrier_t *barrier);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif