Miscellaneous sys/ucontext.h namespace fixes (bug 21457)

[David Miller]

From: Joseph Myers <joseph@codesourcery.com>
Date: Wed, 28 Jun 2017 10:37:45 +0000

> SPARC sys/ucontext.h namespace fixes (bug 21457).
> 
> This patch fixes various miscellaneous namespace issues in the SPARC
> sys/ucontext.h header.  These are similar to changes made previous to
> other sys/ucontext.h headers, where the SPARC header was excluded from
> those previous patches because of its complexity.
> 
> Tested for SPARC with build-many-glibcs.py.

I'm fine with this, please commit.