Add a zlib pkg-config file (more and more ports requires it)

Approved by:	delphij
MFC after:	1 week

lib/libz/Makefile

@@ -66,6 +66,10 @@ test: example minigzip
 	(export LD_LIBRARY_PATH=. ; \
 		echo hello world | ./minigzip | ./minigzip -d )
 
+beforeinstall:
+	${INSTALL} -C -o ${LIBOWN} -g ${LIBGRP} -m ${LIBMODE} \
+		${.CURDIR}/zlib.pc ${DESTDIR}${LIBDATADIR}/pkgconfig
+
 .include <bsd.lib.mk>
 
 ## XXX: clang integrated-as doesn't grok .intel_syntax directives yet

lib/libz/zlib.pc

@@ -0,0 +1,14 @@
+# $FreeBSD$
+prefix=/usr
+exec_prefix=${prefix}
+libdir=${exec_prefix}/lib
+sharedlibdir=${libdir}
+includedir=${prefix}/include
+
+Name: zlib
+Description: zlib compression library
+Version: 1.2.8
+
+Requires:
+Libs: -L${libdir} -L${sharedlibdir} -lz
+Cflags: -I${includedir}