configure: Use pkg-config to handle zlib dependency if possible

Preserves fallback for systems like darwin without zlib.pc

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>

Makefile.am

@@ -66,7 +66,7 @@ libXfont2_la_SOURCES =			\
 
 libXfont2_la_LDFLAGS = -version-number 2:0:0 -no-undefined
 
-libXfont2_la_LIBADD = $(Z_LIBS) $(MATH_LIBS) $(XFONT_LIBS) $(LTLIBOBJS)
+libXfont2_la_LIBADD = $(ZLIB_LIBS) $(Z_LIBS) $(MATH_LIBS) $(XFONT_LIBS) $(LTLIBOBJS)
 
 if XFONT_FONTFILE
 libXfont2_la_SOURCES +=			\

configure.ac

@@ -128,7 +128,12 @@ AC_SUBST(FREETYPE_REQUIRES)
 AC_DEFINE(X_GZIP_FONT_COMPRESSION,1,[Support gzip for bitmap fonts])
 X_GZIP_FONT_COMPRESSION=1
 AC_SUBST(X_GZIP_FONT_COMPRESSION)
-AC_CHECK_LIB(z, gzopen, [Z_LIBS=-lz], AC_MSG_ERROR([*** zlib is required]))
+PKG_CHECK_MODULES(ZLIB, [zlib], [Z_REQUIRES=zlib], [Z_REQUIRES=""])
+if test "x$Z_REQUIRES" = "x"; then
+	AC_CHECK_LIB(z, gzopen, [Z_LIBS=-lz],
+		AC_MSG_ERROR([*** zlib is required]))
+fi
+AC_SUBST(Z_REQUIRES)
 
 AC_ARG_WITH(bzip2,
 	AS_HELP_STRING([--with-bzip2],

xfont2.pc.in

@@ -7,7 +7,7 @@ Name: Xfont2
 Description: X font Library version 2
 Version: @VERSION@
 Requires: xproto fontsproto
-Requires.private: fontenc @FREETYPE_REQUIRES@
+Requires.private: fontenc @FREETYPE_REQUIRES@ @Z_REQUIRES@
 Cflags: -I${includedir}
 Libs: -L${libdir} -lXfont2
 Libs.private: @Z_LIBS@ -lm