rework std.atomic

* move std.atomic.Atomic to std.atomic.Value
* fix incorrect argument order passed to testing.expectEqual
* make the functions be a thin wrapper over the atomic builtins and
  stick to the naming conventions.
* remove pointless functions loadUnchecked and storeUnchecked. Instead,
  name the field `raw` instead of `value` (which is redundant with the
  type name).
* simplify the tests by not passing every possible combination. Many
  cases were iterating over every possible combinations but then not
  even using the for loop element value!
* remove the redundant compile errors which are already implemented by
  the language itself.
* remove dead x86 inline assembly. this should be implemented in the
  language if at all.

lib/std/debug.zig

@@ -375,7 +375,7 @@ pub fn panicExtra(
 
 /// Non-zero whenever the program triggered a panic.
 /// The counter is incremented/decremented atomically.
-var panicking = std.atomic.Atomic(u8).init(0);
+var panicking = std.atomic.Value(u8).init(0);
 
 // Locked to avoid interleaving panic messages from multiple threads.
 var panic_mutex = std.Thread.Mutex{};
@@ -448,7 +448,7 @@ fn waitForOtherThreadToFinishPanicking() void {
         if (builtin.single_threaded) unreachable;
 
         // Sleep forever without hammering the CPU
-        var futex = std.atomic.Atomic(u32).init(0);
+        var futex = std.atomic.Value(u32).init(0);
         while (true) std.Thread.Futex.wait(&futex, 0);
         unreachable;
     }