sandbox: make LTO available

Make LTO available for sandbox architecture.

Signed-off-by: Marek BehĂșn <marek.behun@nic.cz>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/Kconfig b/arch/Kconfig
index 6c4b81a..c5c03d4 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -101,6 +101,7 @@
 
 config SANDBOX
 	bool "Sandbox"
+	select ARCH_SUPPORTS_LTO
 	select BOARD_LATE_INIT
 	select BZIP2
 	select CMD_POWEROFF