langref: clarify allowed atomic types

Floats are not allowed in @cmpxchg

Packed structs are allowed for all atomic builtins

Author: gooncreeper

doc/langref.html.in

@@ -4319,7 +4319,7 @@ comptime {
       </p>
       <p>
       {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#}, a float,
-      an integer or an enum.
+      an integer, an enum, or a packed struct.
       </p>
       <p>{#syntax#}AtomicOrder{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicOrder{#endsyntax#}.</p>
       {#see_also|@atomicStore|@atomicRmw||@cmpxchgWeak|@cmpxchgStrong#}
@@ -4333,7 +4333,7 @@ comptime {
       </p>
       <p>
       {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#}, a float,
-      an integer or an enum.
+      an integer, an enum, or a packed struct.
       </p>
       <p>{#syntax#}AtomicOrder{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicOrder{#endsyntax#}.</p>
       <p>{#syntax#}AtomicRmwOp{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicRmwOp{#endsyntax#}.</p>
@@ -4347,7 +4347,7 @@ comptime {
       </p>
       <p>
       {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#}, a float,
-      an integer or an enum.
+      an integer, an enum, or a packed struct.
       </p>
       <p>{#syntax#}AtomicOrder{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicOrder{#endsyntax#}.</p>
       {#see_also|@atomicLoad|@atomicRmw|@cmpxchgWeak|@cmpxchgStrong#}
@@ -4576,8 +4576,8 @@ comptime {
       more efficiently in machine instructions.
       </p>
       <p>
-      {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#}, a float,
-      an integer or an enum.
+      {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#},
+      an integer, an enum, or a packed struct.
       </p>
       <p>{#syntax#}@typeInfo(@TypeOf(ptr)).pointer.alignment{#endsyntax#} must be {#syntax#}>= @sizeOf(T).{#endsyntax#}</p>
       <p>{#syntax#}AtomicOrder{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicOrder{#endsyntax#}.</p>
@@ -4608,8 +4608,8 @@ fn cmpxchgWeakButNotAtomic(comptime T: type, ptr: *T, expected_value: T, new_val
       However if you need a stronger guarantee, use {#link|@cmpxchgStrong#}.
       </p>
       <p>
-      {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#}, a float,
-      an integer or an enum.
+      {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#},
+      an integer, an enum, or a packed struct.
       </p>
       <p>{#syntax#}@typeInfo(@TypeOf(ptr)).pointer.alignment{#endsyntax#} must be {#syntax#}>= @sizeOf(T).{#endsyntax#}</p>
       <p>{#syntax#}AtomicOrder{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicOrder{#endsyntax#}.</p>