depends: add a zlib build

qt5.7 changed the location of some of its symbols, creating a circular
dependency in Qt5Core. Rather than trying to fix that up, build our own zlib
rather than having it built for us.

depends/packages/qt.mk

@@ -4,7 +4,7 @@ $(package)_download_path=http://download.qt.io/official_releases/qt/5.7/$($(pack
 $(package)_suffix=opensource-src-$($(package)_version).tar.gz
 $(package)_file_name=qtbase-$($(package)_suffix)
 $(package)_sha256_hash=95f83e532d23b3ddbde7973f380ecae1bac13230340557276f75f2e37984e410
-$(package)_dependencies=openssl
+$(package)_dependencies=openssl zlib
 $(package)_linux_dependencies=freetype fontconfig libxcb libX11 xproto libXext
 $(package)_build_subdir=qtbase
 $(package)_qt_libs=corelib network widgets gui plugins testlib
@@ -73,7 +73,7 @@ $(package)_config_opts += -prefix $(host_prefix)
 $(package)_config_opts += -qt-libpng
 $(package)_config_opts += -qt-libjpeg
 $(package)_config_opts += -qt-pcre
-$(package)_config_opts += -qt-zlib
+$(package)_config_opts += -system-zlib
 $(package)_config_opts += -reduce-exports
 $(package)_config_opts += -static
 $(package)_config_opts += -silent