#584 _chsize not defined in unistd.h when using ftruncate

[ralph engels]

Ran into this bug some times over when functions call ftruncate the compiler will throw an error about _chsize
not being defined. So i looked it up in the headers and its located in io.h which is include by unistd.h but the compiler still refuses to acknowlage it ?. this happens with both gcc-5.4.0 and gcc-6.2.0. Im kinda at a loss as to why it seems to not pick it up, any help would be welcome.