No it's not the default compiler, because that one doesn't work.
I have hlcsg, hlbsp, hlvis and hlrad as .exe files from a download.
I drag and drop the files on there to run them, check if there are no errors and then run it in cs 1.6 or cs cz.
Edit: Yes its in a block with Sky texture. The Sky texture is currently from HLbasics.wad i dont know which .wad has another sky