[libpng17] Port recent zlib windowBits handling from libpng-1.6.3beta06

pngpriv.h

@@ -629,6 +629,24 @@
 #include "pngstruct.h"
 #include "pnginfo.h"
 
+/* Validate the include paths - the include path used to generate pnglibconf.h
+ * must match that used in the build, or we must be using pnglibconf.h.prebuilt:
+ */
+#if PNG_ZLIB_VERNUM != 0 && PNG_ZLIB_VERNUM != ZLIB_VERNUM
+#  error ZLIB_VERNUM != PNG_ZLIB_VERNUM \
+      "-I (include path) error: see the notes in pngpriv.h"
+   /* This means that when pnglibconf.h was built the copy of zlib.h that it
+    * used is not the same as the one being used here.  Because the build of
+    * libpng makes decisions to use inflateInit2 and inflateReset2 based on the
+    * zlib version number and because this affects handling of certain broken
+    * PNG files the -I directives must match.
+    *
+    * The most likely explanation is that you passed a -I in CFLAGS, this will
+    * not work; all the preprocessor directories and in particular all the -I
+    * directives must be in CPPFLAGS.
+    */
+#endif
+
 /* This is used for 16 bit gamma tables -- only the top level pointers are
  * const; this could be changed:
  */