x86: Add a dummy setjmp implementation for x86_64

We don't have the code for this yet. Add a dummy version for now, so that
EFI builds correctly.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/cpu/x86_64/Makefile

@@ -3,4 +3,4 @@
 # Written by Simon Glass <sjg@chromium.org>
 #
 
-obj-y += cpu.o interrupts.o
+obj-y += cpu.o interrupts.o setjmp.o

arch/x86/cpu/x86_64/setjmp.c

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2016 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <asm/setjmp.h>
+
+int setjmp(struct jmp_buf_data *jmp_buf)
+{
+	printf("WARNING: setjmp() is not supported\n");
+
+	return 0;
+}
+
+void longjmp(struct jmp_buf_data *jmp_buf, int val)
+{
+	printf("WARNING: longjmp() is not supported\n");
+}