package/musl: enable on s390x

Add s390x musl supported archs. Upstream musl already supports s390x[1].

Tested with qemu_s390s_defconfig:

	$ output/host/bin/qemu-system-s390x -M s390-ccw-virtio -cpu max,zpci=on -m 4G -smp 2 -kernel output/bzImage -drive file=output/images/rootfs.ext2,if=virtio,format=raw -append "rootwait root=/dev/vda net.ifnames=0 biosdevname=0" -display none -serial mon:stdio -net nic,model=virtio -net user
	(...)
	Welcome to Buildroot
	buildroot login: root
	# uname -a
	Linux buildroot 6.1.44 #2 SMP Sun Feb 18 01:33:42 CET 2024 s390x GNU/Linux
	# /lib/ld-musl-s390x.so.1
	musl libc (s390x)
	Version 1.2.4
	Dynamic Program Loader
	Usage: /lib/ld-musl-s390x.so.1 [options] [--] pathname [args]

[1]: https://git.musl-libc.org/cgit/musl/commit/?id=15094943050eb9a564f409323070e50b40f78816

Signed-off-by: Gaël PORTAY <gael.portay@rtone.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

Author: gportay

package/musl/Config.in

@@ -16,6 +16,7 @@ config BR2_PACKAGE_MUSL_ARCH_SUPPORTS
 	default y if BR2_powerpc64
 	default y if BR2_powerpc64le
 	default y if BR2_riscv
+	default y if BR2_s390x
 	default y if BR2_sh
 	default y if BR2_x86_64
 	depends on !BR2_POWERPC_CPU_HAS_SPE # not supported, build breaks