sandbox: barebox executable for x86_64 is nonfunctional

[Peter Mamonov]

Hello, Ahmad,

After 54d47eb7e "sandbox: support forcing 32-bit x86" the sandbox barebox 
executable produced on x86_64 host is nonfunctional, i.e. it exits right after 
start. Reverting the mentioned commit does fix the problem.  The host is 
running a bit outdated Debian bullseye/sid, gcc version is "gcc (Debian 9.2.1-19) 9.2.1 
20191109". Here are the commands I've used to build and run barebox:

	$ export ARCH=sandbox
	$ make mrproper && make sandbox_defconfig && make -j4 -s
	$ ./barebox
	$ echo $?
	1

Regards,
Peter