meson: add a zlib subproject

To help windows build

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>

meson.build

@@ -1139,7 +1139,7 @@ else
 endif
 
 # TODO: some of these may be conditional
-dep_zlib = dependency('zlib', version : '>= 1.2.3')
+dep_zlib = dependency('zlib', version : '>= 1.2.3', fallback : ['zlib', 'zlib_dep'])
 pre_args += '-DHAVE_ZLIB'
 dep_thread = dependency('threads')
 if dep_thread.found() and host_machine.system() != 'windows'