disas: Configure capstone for aarch64 host without libvixl

The ifdef tangle failed to set cap_arch if libvixl itself
was not configured (e.g. due to lack of c++ compiler).

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

disas.c

@@ -430,9 +430,11 @@ static void initialize_debug_host(CPUDebug *s)
 #else
 #error unsupported RISC-V ABI
 #endif
-#elif defined(__aarch64__) && defined(CONFIG_ARM_A64_DIS)
-    s->info.print_insn = print_insn_arm_a64;
+#elif defined(__aarch64__)
     s->info.cap_arch = CS_ARCH_ARM64;
+# ifdef CONFIG_ARM_A64_DIS
+    s->info.print_insn = print_insn_arm_a64;
+# endif
 #elif defined(__alpha__)
     s->info.print_insn = print_insn_alpha;
 #elif defined(__sparc__)