[PATCH lib/libXpm] Define NO_ZPIPE when building for MinGW

[Colin Harrison]

Hi,

> Ángel González wrote: There's no reason for decompression via pipe not to
work under Windows.

Luckily I haven't found an instance where I use libXpm, in anger, to
decompress an XPM file via a pipe on Windows
...until I can find a useful/modern/test case (and hence motivation to write
code) I lazily just like it to compile :)

Thanks,
Colin Harrison