std.Target: baseline model for s390x-zos should be arch10, not arch8

Author: alexrp

lib/std/Target.zig

@@ -1912,7 +1912,11 @@ pub const Cpu = struct {
                 .powerpc64le => &powerpc.cpu.ppc64le,
                 .riscv32, .riscv32be => &riscv.cpu.baseline_rv32,
                 .riscv64, .riscv64be => &riscv.cpu.baseline_rv64,
-                .s390x => &s390x.cpu.arch8, // gcc/clang do not have a generic s390x model.
+                // gcc/clang do not have a generic s390x model.
+                .s390x => switch (os.tag) {
+                    .zos => &s390x.cpu.arch10,
+                    else => &s390x.cpu.arch8,
+                },
                 .sparc => &sparc.cpu.v9, // glibc does not work with 'plain' v8.
                 .sparc64 => switch (os.tag) {
                     .solaris => &sparc.cpu.ultrasparc3,