qemu/atomic.h: rename atomic_ to qatomic_

clang's C11 atomic_fetch_*() functions only take a C11 atomic type
pointer argument. QEMU uses direct types (int, etc) and this causes a
compiler error when a QEMU code calls these functions in a source file
that also included <stdatomic.h> via a system header file:

  $ CC=clang CXX=clang++ ./configure ... && make
  ../util/async.c:79:17: error: address argument to atomic operation must be a pointer to _Atomic type ('unsigned int *' invalid)

Avoid using atomic_*() names in QEMU's atomic.h since that namespace is
used by <stdatomic.h>. Prefix QEMU's APIs with 'q' so that atomic.h
and <stdatomic.h> can co-exist. I checked /usr/include on my machine and
searched GitHub for existing "qatomic_" users but there seem to be none.

This patch was generated using:

  $ git grep -h -o '\<atomic\(64\)\?_[a-z0-9_]\+' include/qemu/atomic.h | \
    sort -u >/tmp/changed_identifiers
  $ for identifier in $(</tmp/changed_identifiers); do
        sed -i "s%\<$identifier\>%q$identifier%g" \
            $(git grep -I -l "\<$identifier\>")
    done

I manually fixed line-wrap issues and misaligned rST tables.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20200923105646.47864-1-stefanha@redhat.com>

util/qemu-coroutine.c

@@ -60,7 +60,7 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque)
                  * release_pool_size and the actual size of release_pool.  But
                  * it is just a heuristic, it does not need to be perfect.
                  */
-                alloc_pool_size = atomic_xchg(&release_pool_size, 0);
+                alloc_pool_size = qatomic_xchg(&release_pool_size, 0);
                 QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool);
                 co = QSLIST_FIRST(&alloc_pool);
             }
@@ -88,7 +88,7 @@ static void coroutine_delete(Coroutine *co)
     if (CONFIG_COROUTINE_POOL) {
         if (release_pool_size < POOL_BATCH_SIZE * 2) {
             QSLIST_INSERT_HEAD_ATOMIC(&release_pool, co, pool_next);
-            atomic_inc(&release_pool_size);
+            qatomic_inc(&release_pool_size);
             return;
         }
         if (alloc_pool_size < POOL_BATCH_SIZE) {
@@ -115,7 +115,7 @@ void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co)
 
         /* Cannot rely on the read barrier for to in aio_co_wake(), as there are
          * callers outside of aio_co_wake() */
-        const char *scheduled = atomic_mb_read(&to->scheduled);
+        const char *scheduled = qatomic_mb_read(&to->scheduled);
 
         QSIMPLEQ_REMOVE_HEAD(&pending, co_queue_next);