selftests/bpf: Add __arch_s390x macro

Make it possible to limit certain tests to s390x, just like it's
already done for x86_64, arm64, and riscv64.

Signed-off-by: Ilya Leoshkevich <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/progs/bpf_misc.h

···
 #define __arch_x86_64		__arch("X86_64")
 #define __arch_arm64		__arch("ARM64")
 #define __arch_riscv64		__arch("RISCV64")
+#define __arch_s390x		__arch("s390x")
 #define __caps_unpriv(caps)	__attribute__((btf_decl_tag("comment:test_caps_unpriv=" EXPAND_QUOTE(caps))))
 #define __load_if_JITed()	__attribute__((btf_decl_tag("comment:load_mode=jited")))
 #define __load_if_no_JITed()	__attribute__((btf_decl_tag("comment:load_mode=no_jited")))

tools/testing/selftests/bpf/test_loader.c

···
 	ARCH_X86_64	= 0x2,
 	ARCH_ARM64	= 0x4,
 	ARCH_RISCV64	= 0x8,
+	ARCH_S390X	= 0x10,
 };
 
 static int get_current_arch(void)
···
 	return ARCH_ARM64;
 #elif defined(__riscv) && __riscv_xlen == 64
 	return ARCH_RISCV64;
+#elif defined(__s390x__)
+	return ARCH_S390X;
 #endif
 	return ARCH_UNKNOWN;
 }
···
 				arch = ARCH_ARM64;
 			} else if (strcmp(val, "RISCV64") == 0) {
 				arch = ARCH_RISCV64;
+			} else if (strcmp(val, "s390x") == 0) {
+				arch = ARCH_S390X;
 			} else {
 				PRINT_FAIL("bad arch spec: '%s'\n", val);
 				err = -EINVAL;