x86/compat: don't set has_compat_sigreturn if !CONFIG_COMPAT

We can be on v4.9 or newer kernel, but have no 32-bit multilib
toolchain, which will result in !CONFIG_COMPAT but
kdat_compat_sigreturn_test() will return true as we have
new arch_prctls in kernel needed for compatible C/R.
Fail compat test in this case.

travis-ci: success for 32-bit tests fixes
Reported-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/arch/x86/crtools.c

@@ -30,6 +30,7 @@
 #ifdef CONFIG_X86_64
 int kdat_compat_sigreturn_test(void)
 {
+#ifdef CONFIG_COMPAT
 	unsigned long auxval;
 	int ret;
 
@@ -46,6 +47,7 @@ int kdat_compat_sigreturn_test(void)
 	ret = syscall(SYS_arch_prctl, ARCH_MAP_VDSO_32, 1);
 	if (ret == -1 && errno == EEXIST)
 		return 1;
+#endif
 	return 0;
 }
 #endif /* CONFIG_X86_64 */