RFR: JDK-8196911: Windows build fails with not finding zlib.h

[Tim Bell]

Erik:

> A small typo managed to sneak itself into my previous patch, causing the
> build to fail on Windows.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8196911
[...snip...]
> -  if test "x$USER_EXTERNAL_LIBZ" = "xfalse"; then
> +  if test "x$USE_EXTERNAL_LIBZ" = "xfalse"; then

Looks good.  I missed that one myself as a reviewer.

/Tim