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/atomic64.c

@@ -51,8 +51,8 @@ static QemuSpin *addr_to_lock(const void *addr)
         return ret;                             \
     }
 
-GEN_READ(atomic_read_i64, int64_t)
-GEN_READ(atomic_read_u64, uint64_t)
+GEN_READ(qatomic_read_i64, int64_t)
+GEN_READ(qatomic_read_u64, uint64_t)
 #undef GEN_READ
 
 #define GEN_SET(name, type)                     \
@@ -65,11 +65,11 @@ GEN_READ(atomic_read_u64, uint64_t)
         qemu_spin_unlock(lock);                 \
     }
 
-GEN_SET(atomic_set_i64, int64_t)
-GEN_SET(atomic_set_u64, uint64_t)
+GEN_SET(qatomic_set_i64, int64_t)
+GEN_SET(qatomic_set_u64, uint64_t)
 #undef GEN_SET
 
-void atomic64_init(void)
+void qatomic64_init(void)
 {
     int i;