pngquant.patch

    diff -ur pngquant-2.9.0/configure pngquant-2.9.0.fixed/configure
--- pngquant-2.9.0/configure    2017-03-06 09:37:30.000000000 +0100
+++ pngquant-2.9.0.fixed/configure  2017-03-07 09:57:20.246012152 +0100
@@ -48,6 +48,7 @@
         help "--with-cocoa/--without-cocoa  use Cocoa framework to read images"
 fi
         help "--with-libpng=<dir>           search for libpng in directory"
+        help "--with-zlib=<dir>             search for zlib in directory"
         echo
         help "CC=<compiler>                 use given compiler command"
         help "CFLAGS=<flags>                pass options to the compiler"
@@ -97,6 +98,9 @@
     --with-libpng=*)
         LIBPNG_DIR=${i#*=}
         ;;
+    --with-zlib=*)
+        ZLIB_DIR=${i#*=}
+        ;;
     --prefix=*)
         PREFIX=${i#*=}
         ;;
@@ -238,6 +242,19 @@
     echo "${MAJ}${MIN}"
 }

+# returns full zlib.h version string
+zlibh_string() {
+    echo "$(grep -m1 "define ZLIB_VERSION" "$1" | \
+            grep -Eo '"[^"]+"' | grep -Eo '[^"]+')"
+}
+
+# returns major minor version numbers from png.h
+zlibh_majmin() {
+    local MAJ=$(grep -m1 "define ZLIB_VER_MAJOR" "$1" | grep -Eo "[0-9]+")
+    local MIN=$(grep -m1 "define ZLIB_VER_MINOR" "$1" | grep -Eo "[0-9]+")
+    echo "${MAJ}${MIN}"
+}