sandbox: Add function os_flush()

It flushes stdout.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/sandbox/cpu/os.c

@@ -669,6 +669,11 @@ void os_puts(const char *str)
 		os_putc(*str++);
 }
 
+void os_flush(void)
+{
+	fflush(stdout);
+}
+
 int os_write_ram_buf(const char *fname)
 {
 	struct sandbox_state *state = state_get_current();

include/os.h

@@ -295,6 +295,14 @@ void os_putc(int ch);
  */
 void os_puts(const char *str);
 
+/**
+ * os_flush() - flush controlling OS terminal
+ *
+ * This bypasses the U-Boot console support and flushes directly the OS
+ * stdout file descriptor.
+ */
+void os_flush(void);
+
 /**
  * os_write_ram_buf() - write the sandbox RAM buffer to a existing file
  *