[PATCH 0/4] Provide C11 atomic operations

[Torvald Riegel <triegel at redhat dot com>]

This patch set provides support for C11-like atomic operations.  It does
not change existing code that that uses the current atomic ops, so
callers of atomic ops can be changed one algorithm at a time.  (To
illustrate such changes, the last patch transforms pthread_once to use
C11 atomics.)

The atomic ops all have C11 semantics but use different names to avoid
naming collisions with C11 operations.  If we should require C11
compilation at some time in the future, transforming the calls of all
atomic operations will be easy.

This expects, of course, that we use the C11 model.  The only difference
is that I've chosen to not explicitly use atomic types, but rather just
use atomic operations on plain data types.  This will work for existing
code that is transformed.  For new code, it can mean that programmers
have to be careful to use the right alignment if the atomic ops on a
particular arch come with such constraints.
If we get consensus for that, we can change to using atomic types in a
second phase.

After acceptance of this patch set, I can provide additional
documentation on the wiki.  However, I'd like to get some input on how
much (ie, how much detail, etc.) documentation you would like to see.
One reason to move to C11 is to not have contributors have to learn
something new, so I guess that the glibc-specific documentation we'd
need would be rather small in size.