libc: io: implement (v)fprintf

lib/libc/io/stdio/fprintf.c

@@ -1,6 +1,13 @@
 #include "file.h"
 
+#include <stdio.h>
+
 int fprintf(struct __opaque_file *stream, const char *format, ...)
 {
-	return 0;
+	va_list arg;
+	va_start(arg, format);
+	int ret = vfprintf(stream, format, arg);
+	va_end(arg);
+
+	return ret;
 }