Provide a copy of stdout_isatty() on CloudABI.
Provide a copy of stdout_isatty() on CloudABI.

CloudABI doesn't make any distinction between TTYs and ordinary pipes.
While there, remove the redundant implementation used by Redox. It can
use the same stub function.

aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust