The GNU C Library will be rebased in F21 to match glibc 2.20.

[Bruno Wolff III]

On Thu, Jul 31, 2014 at 23:05:21 +0530,
  Siddhesh Poyarekar <siddhesh at redhat.com> wrote:
>
>the latest commit.  I've been doing regular rebases for a while now
>(almost a year AFAICT) and IIRC we have had just one serious problem
>last week where i686 boxes got bricked.  In the end it was found to be
>a gcc bug that miscompiled some code in glibc.

If you figured out what was going on in time you could even recover 
with a yum downgrade in you had a root shell open (which I was able to do).
So not everyone using i686 got their machines bricked.