configure.ac: define WL_HIDE_DEPRECATED at global scale

configure.ac: define WL_HIDE_DEPRECATED at global scale

Due to GCC feature described in previous commit, the expected
deprecation warnings may be missing.

Set the WL_HIDE_DEPRECATED macro which will omit the deprecated
functionality, resulting in more distinct build issues.

That is safe since the symbols guarded within the macro is static.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Suggested-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniels@collabora.com>