disas: Fix build against Capstone v6 (again)

Like 9971cbac2f3, which set CAPSTONE_AARCH64_COMPAT_HEADER,
also set CAPSTONE_SYSTEMZ_COMPAT_HEADER.  Fixes the build
against capstone v6-alpha.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Gustavo Romero <gustavo.romero@linaro.org>
Message-id: 20241022013047.830273-1-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

include/disas/capstone.h

@@ -4,6 +4,7 @@
 #ifdef CONFIG_CAPSTONE
 
 #define CAPSTONE_AARCH64_COMPAT_HEADER
+#define CAPSTONE_SYSTEMZ_COMPAT_HEADER
 #include <capstone.h>
 
 #else