contrib: add zlib rules

Dependency required by libav.

Based on VideoLan code by Jean-Baptiste Kempf et al.
Refs: #46617

Change-Id: I7284ee572805da5d1eb3933f79fc30d4ba9b40c0

contrib/src/zlib/SHA512SUMS

+ece209d4c7ec0cb58ede791444dc754e0d10811cbbdebe3df61c0fd9f9f9867c1c3ccd5f1827f847c005e24eef34fb5bf87b5d3f894d75da04f1797538290e4a  zlib-1.2.8.tar.gz

contrib/src/zlib/rules.mak

+# ZLIB
+ZLIB_VERSION := 1.2.8
+ZLIB_URL := $(SF)/libpng/zlib-$(ZLIB_VERSION).tar.gz
+
+PKGS += zlib
+ifeq ($(call need_pkg,"zlib"),)
+PKGS_FOUND += zlib
+endif
+
+ifeq ($(shell uname),Darwin) # zlib tries to use libtool on Darwin
+ifdef HAVE_CROSS_COMPILE
+ZLIB_CONFIG_VARS=CHOST=$(HOST)
+endif
+endif
+
+$(TARBALLS)/zlib-$(ZLIB_VERSION).tar.gz:
+	$(call download,$(ZLIB_URL))
+
+.sum-zlib: zlib-$(ZLIB_VERSION).tar.gz
+
+zlib: zlib-$(ZLIB_VERSION).tar.gz .sum-zlib
+	$(UNPACK)
+	$(MOVE)
+
+.zlib: zlib
+	cd $< && $(HOSTVARS) $(ZLIB_CONFIG_VARS) ./configure --prefix=$(PREFIX) --static
+	cd $< && $(MAKE) install
+	touch $@