accept freebsd targets

http://bugs.gentoo.org/316841

--- zlib-1.2.5/configure
+++ zlib-1.2.5/configure
@@ -118,7 +118,7 @@
     uname=`(uname -s || echo unknown) 2>/dev/null`
   fi
   case "$uname" in
-  Linux* | linux* | GNU | GNU/* | *BSD | DragonFly) LDSHARED=${LDSHARED-"$cc -shared -Wl,-soname,libz.so.1,--version-script,zlib.map"} ;;
+  Linux* | linux* | GNU | GNU/* | *BSD | DragonFly | freebsd* ) LDSHARED=${LDSHARED-"$cc -shared -Wl,-soname,libz.so.1,--version-script,zlib.map"} ;;
   CYGWIN* | Cygwin* | cygwin* | OS/2*)
         EXE='.exe' ;;
   MINGW*|mingw*)