sandbox: make LTO available

Make LTO available for sandbox architecture.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/Kconfig

@@ -101,6 +101,7 @@ config RISCV
 
 config SANDBOX
 	bool "Sandbox"
+	select ARCH_SUPPORTS_LTO
 	select BOARD_LATE_INIT
 	select BZIP2
 	select CMD_POWEROFF

arch/sandbox/config.mk

@@ -17,16 +17,20 @@ PLATFORM_CPPFLAGS += $(shell $(SDL_CONFIG) --cflags)
 endif
 
 cmd_u-boot__ = $(CC) -o $@ -Wl,-T u-boot.lds $(u-boot-init) \
+	$(LTO_FINAL_LDFLAGS) \
 	-Wl,--whole-archive \
 		$(u-boot-main) \
+		$(u-boot-keep-syms-lto) \
 	-Wl,--no-whole-archive \
 	$(PLATFORM_LIBS) -Wl,-Map -Wl,u-boot.map
 
 cmd_u-boot-spl = (cd $(obj) && $(CC) -o $(SPL_BIN) -Wl,-T u-boot-spl.lds \
+	$(LTO_FINAL_LDFLAGS) \
 	$(patsubst $(obj)/%,%,$(u-boot-spl-init)) \
 	-Wl,--whole-archive \
 		$(patsubst $(obj)/%,%,$(u-boot-spl-main)) \
 		$(patsubst $(obj)/%,%,$(u-boot-spl-platdata)) \
+		$(patsubst $(obj)/%,%,$(u-boot-spl-keep-syms-lto)) \
 	-Wl,--no-whole-archive \
 	$(PLATFORM_LIBS) -Wl,-Map -Wl,u-boot-spl.map -Wl,--gc-sections)