pkg-config zlib check in 3c13bc

[David Bremner]

Tomi Ollila <tomi.ollila at iki.fi> writes:

>
> But, I'd like suggest alternate option to create a test c program
> and test whether it compiles (analogous to what there is already
> done with many other checks) -- this same would apply to fdatasync()
> case too.
>

I agree in principle, but I'm not sure it's detectable at compile time,
since the option we need is passed as a string (boo!).  

I guess the ZLIB_VERNUM hack would be preferable to adding platform
specific checks to configure. But note you'd need somehow to find
zlib.h.

See my other patch for fdatasync.

d