Revert of Revert of Small refactor around futex.h. (patchset #1 id:1 of https://coder...

Revert of Revert of Small refactor around futex.h. (patchset #1 id:1 of https://codereview.chromium.org/1084173003/)

Reason for revert:
Sorry, mistake on my part, this CL isn't the cause.

Original issue's description:
> Revert of Small refactor around futex.h. (patchset #1 id:20001 of https://codereview.chromium.org/1076213002/)
>
> Reason for revert:
> Breaks ChromeOS veyron_jerry boot.
>
> BUG=477352
>
> Original issue's description:
> > Small refactor around futex.h.
> >
> > This is the preparation of seccomp-bpf implementation
> > for nacl_helper_nonsfi.
> > PNaCl toolchain does not provides linux/futex.h.
> > This CL is the preparation to reuse android_futex.h
> > for PNaCl toolchain, too.
> >
> > TEST=Ran bots.
> > BUG=358465
> >
> > Committed: https://crrev.com/3b996212fa3c92af3233246ae54af728eb7c3591
> > Cr-Commit-Position: refs/heads/master@{#324996}
>
> TBR=mdempsky@chromium.org,hidehiko@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=358465
>
> Committed: https://crrev.com/4c05c94295ee26adffe966678719085f02b15f2f
> Cr-Commit-Position: refs/heads/master@{#325265}

TBR=mdempsky@chromium.org,hidehiko@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=477352

Review URL: https://codereview.chromium.org/1088253002

Cr-Commit-Position: refs/heads/master@{#325268}