Add numbering rule for lambdas in class bodies outside of default

arguments and default member initializers.

Author: zygoloid

abi.html

@@ -5570,6 +5570,7 @@ <h4><a href="#closure-types">5.1.8 Closure Types (Lambdas)</a></h4>
 <li>default member initializers</li>
 <li>the bodies of inline or templated functions</li>
 <li>the initializers of inline or templated variables</li>
+<li>the remaining contexts in class definitions</li>
 </ul>
 
 In all these contexts, the encoding of the closure types builds on an
@@ -5658,6 +5659,28 @@ <h4><a href="#closure-types">5.1.8 Closure Types (Lambdas)</a></h4>
 	  // Corresponding operator(): _ZNK1SIiE1xMUlvE_clEv
 </pre></code>
 
+<p>
+If the context is within a class definition,
+and not within one of the above more specific cases,
+the closure class and its members are encoded as follows:
+<code><pre><font color=blue>  &lt;<a href="#mangle.local-name">local-name</a>&gt; ::= Z &lt;<i>class</i> <a href="#mangle.name">name</a>&gt; E &lt;<i>entity</i> <a href="#mangle.name">name</a>&gt;
+</font></pre></code>
+As above, the <code>&lt;<i>entity</i> <a href="#mangle.name">name</a>&gt;</code> will contain a
+<code>&lt;<a href="#mangle.closure-type-name">closure-type-name</a>&gt;</code>,
+which is numbered within the class, counting only those closure types for which
+this mangling rule applies.
+For example:
+<code><pre>
+	struct S {
+	  // Template argument is LZ1SEUlvE_E; f&lt;true&gt; is _ZN1S1fILb1EEEv1XILZ1SEUlvE_EE
+	  template&lt;bool B&gt; void f(X&lt;[]{ return B; }()&gt;) { ... }
+	  int n = []{ return 0; }(); // not counted towards numbering in struct S
+	  // Template argument is LZ1SEUlvE0_E; f&lt;true&gt; is _ZN1S1fILb1EEEv1XILZ1SEUlvE0_EE
+	  template&lt;bool B&gt; void f(X&lt;[]{ return !B; }()&gt;) { ... }
+	};
+</pre></code>
+
+
 <p>
 In a generic lambda, uses of <code>auto</code> in the parameter list
 are mangled as the corresponding artificial template type parameter.