tests/tcg: add a simple s390x test

Copied from alpha.

Signed-off-by: Pavel Zbitskiy <pavel.zbitskiy@gmail.com>
Message-Id: <20180821025104.19604-2-pavel.zbitskiy@gmail.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

MAINTAINERS

@@ -253,6 +253,7 @@ S: Maintained
 F: target/s390x/
 F: hw/s390x/
 F: disas/s390.c
+F: tests/tcg/s390x/
 L: qemu-s390x@nongnu.org
 
 SH4

tests/tcg/s390x/Makefile.target

+VPATH+=$(SRC_PATH)/tests/tcg/s390x
+CFLAGS+=-march=zEC12 -m64
+TESTS+=hello-s390x

tests/tcg/s390x/hello-s390x.c

+#include <unistd.h>
+
+int main(void)
+{
+    write(1, "hello\n", 6);
+    return 0;
+}