libc/stream: provide lowerout_stream default initialization function

Signed-off-by: yinshengkai <yinshengkai@xiaomi.com>

include/nuttx/streams.h

@@ -309,6 +309,8 @@ extern "C"
 #  define EXTERN extern
 #endif
 
+extern struct lib_outstream_s g_lowoutstream;
+
 /****************************************************************************
  * Public Function Prototypes
  ****************************************************************************/

libs/libc/stream/lib_lowoutstream.c

@@ -33,6 +33,26 @@
 
 #include "libc.h"
 
+/****************************************************************************
+ * Private Functions Prototypes
+ ****************************************************************************/
+
+static void lowoutstream_putc(FAR struct lib_outstream_s *self, int ch);
+static int lowoutstream_puts(FAR struct lib_outstream_s *self,
+                             FAR const void *buf, int len);
+
+/****************************************************************************
+ * Public Data
+ ****************************************************************************/
+
+struct lib_outstream_s g_lowoutstream =
+{
+  0,
+  lowoutstream_putc,
+  lowoutstream_puts,
+  lib_noflush
+};
+
 /****************************************************************************
  * Private Functions
  ****************************************************************************/