android,configure,meson: define HAVE_ZLIB

The next change wants to use some optional zlib functionality, however
not all platforms currently use zlib. Based on earlier Jordan Justen's
patches and their review feedback.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
diff --git a/meson.build b/meson.build
index 77e4e89..ae31cdd 100644
--- a/meson.build
+++ b/meson.build
@@ -943,6 +943,7 @@
 
 # TODO: some of these may be conditional
 dep_zlib = dependency('zlib', version : '>= 1.2.3')
+pre_args += '-DHAVE_ZLIB'
 dep_thread = dependency('threads')
 if dep_thread.found() and host_machine.system() != 'windows'
   pre_args += '-DHAVE_PTHREAD'