use system zlib under Mac

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@18247 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

configure.in

@@ -1697,11 +1697,20 @@ if test "$wxUSE_ZLIB" != "no" ; then
     AC_DEFINE(wxUSE_ZLIB)
 
     if test "$wxUSE_ZLIB" = "sys" -o "$wxUSE_ZLIB" = "yes" ; then
-        dnl we have troubles with ancient zlib versions (e.g. 1.0.4 is known
+        dnl don't test for zlib under Mac -- its verson there is 1.1.3 but we
-        dnl to not work) and although I don't know which is the minimal
+        dnl should still use it because hopefully (can someone confirm this?)
-        dnl required version it's safer to test for 1.1.4 as it fixes a
+        dnl Apple did fix the security problem in it and not using the system
-        dnl security problem in 1.1.3 -- and hopefully nobody has anything
+        dnl library results in a whole bunch of warnings when linking with
-        dnl more ancient (1.1.3 was released in July 1998) anyow
+        dnl Carbon framework
+        if test "$USE_DARWIN" = 1; then
+            system_zlib_h_ok="yes"
+        else
+            dnl we have troubles with ancient zlib versions (e.g. 1.0.4 is
+            dnl known to not work) and although I don't know which is
+            dnl the minimal required version it's safer to test for 1.1.4 as
+            dnl it fixes a security problem in 1.1.3 -- and hopefully nobody
+            dnl has anything more ancient (1.1.3 was released in July 1998)
+            dnl anyhow
             AC_CACHE_CHECK([for zlib.h >= 1.1.4], ac_cv_header_zlib_h,
                 AC_TRY_RUN(
                     [
@@ -1731,7 +1740,10 @@ if test "$wxUSE_ZLIB" != "no" ; then
                 )
             )
 
-        if test "$ac_cv_header_zlib_h" = "yes"; then
+            system_zlib_h_ok=$ac_cv_header_zlib_h
+        fi
+
+        if test "$system_zlib_h_ok" = "yes"; then
             AC_CHECK_LIB(z, deflate, ZLIB_LINK=" -lz")
         fi