linux-user/aarch64: Add vdso

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/meson.build

@@ -35,6 +35,7 @@ gen_vdso_exe = executable('gen-vdso', 'gen-vdso.c',
 gen_vdso = generator(gen_vdso_exe, output: '@BASENAME@.c.inc',
                      arguments: ['-o', '@OUTPUT@', '@EXTRA_ARGS@', '@INPUT@'])
 
+subdir('aarch64')
 subdir('alpha')
 subdir('arm')
 subdir('hppa')