Build linux target from Macos.

I tried compiling liunx targets from Macos, but failed.

build.hxml
```haxe
--cpp bin/cpp
--main Main
-D linux
```
```haxe
class Main {
static function main() {
trace("hello world");
}
}
```
error mssage:
```
sh: : command not found
Error: Could not create PCH
Error: Build failed
```

Can tell me how to compile Linux targets from Macos?