configure: avoid using zlib's pkgconfig file, fixes issue 6.
configure: avoid using zlib's pkgconfig file, fixes issue 6.

Not all systems provide a zlib.pc file, so explicitly check for
InflateInit2() which is what we use in XBPS.

Thanks to str1ngs for finding this error on Ubuntu.

ebfe/xbps,ebfe/xbps,datenwolf/xbps,stpx/xbps,ebfe/xbps,stpx/xbps,datenwolf/xbps,datenwolf/xbps,stpx/xbps