add _XOPEN_SOURCE in header file to get the right offset in eager strategy

[kikofernandez]

No description provided.

[kaeluka]

have you talked to @albertnetymk about adding the _XOPEN_SOURCE lines? have you come to an agreement? the commit looks good, but i'm hesitant to merge it as albert seems to think that the line should not go in...

[albertnetymk]

We just discussed this. This commit shall get us to the state that both coroutine and future are working properly on mac and linux. The reason why I claimed xopen is not needed here is that in lazy version (which is WIP) ucontext info is completely hidden in the runtime, and no userspace code would see it.

[EliasC]

Just to get some discussion, shouldn't this line be without parenthesis to follow the surrounding coding style?

[kikofernandez]

You are absolutely right. I'll fix it in another commit

[albertnetymk]

Next time, we should wait for a while before merging. After all, PR is meant for code review & discussion. @EliasC For the style in Haskell file, I think so. For the commented C code, if (0) is kept there so that we could easily, sort of, switch back and forth. The printf line should be removed.

[kaeluka]

What's "a while"?

[albertnetymk]

Don't know exactly how long. Some comments provided by @EliasC should be applied, and rebase should get rid of them, but we didn't do that because insufficent time is provided before merging.