lib_vsprintf: Add %pV format support

test case:
void test(const char *fmt, ...)
{
  struct va_format vaf;
  va_list ap;

  va_start(ap, fmt);
  vaf.fmt = fmt;
  vaf.va = ≈
  printf("func:%s, %pV, line:%d\n", __func__, &vaf, __LINE__);
  va_end(ap);
}

int main(int argc, FAR char *argv[])
{
  char str[] = "Hello Boy and Girl!";
  int count = 10;

  test("%s %d", str, count);
  return 0;
}

>> test
func:test, Hello Boy and Girl! 10, line:49

Change-Id: I6d97515dce3f10a880145a1ff7fcba5e9cbebd37
Signed-off-by: Jiuzhu Dong <dongjiuzhu1@xiaomi.com>

include/stdio.h

@@ -104,6 +104,12 @@
 
 typedef struct file_struct FILE;
 
+struct va_format
+{
+  FAR const char *fmt;
+  FAR va_list *va;
+};
+
 /****************************************************************************
  * Public Data
  ****************************************************************************/

libs/libc/stdio/lib_libvsprintf.c

@@ -117,6 +117,8 @@
 #  define fmt_char(fmt)   (*(fmt)++)
 #endif
 
+#define fmt_ungetc(fmt)   ((fmt)--)
+
 /****************************************************************************
  * Private Types
  ****************************************************************************/
@@ -459,6 +461,17 @@ static int vsprintf_internal(FAR struct lib_outstream_s *stream,
 
       if (c == 'p')
         {
+          if (fmt_char(fmt) == 'V')
+            {
+              FAR struct va_format *vaf = va_arg(ap, void *);
+              vsprintf_internal(stream, NULL, 0, vaf->fmt, *vaf->va);
+              continue;
+            }
+          else
+            {
+              fmt_ungetc(fmt);
+            }
+
           /* Determine size of pointer and set flags accordingly */
 
           flags &= ~(FL_LONG | FL_REPD_TYPE);