add more legacy functions: setlinebuf and setbuffer

src/stdio/setbuf.c

@@ -1,4 +1,4 @@
-#include "stdio_impl.h"
+#include <stdio.h>
 
 void setbuf(FILE *f, char *buf)
 {

src/stdio/setbuffer.c

@@ -0,0 +1,7 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+
+void setbuffer(FILE *f, char *buf, size_t size)
+{
+	setvbuf(f, buf, buf ? _IOFBF : _IONBF, size);
+}

src/stdio/setlinebuf.c

@@ -0,0 +1,7 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+
+void setlinebuf(FILE *f)
+{
+	setvbuf(f, 0, _IOLBF, 0);
+}