Make the template-name in a closure-prefix substitutable.

Author: zygoloid

abi.html

@@ -5870,11 +5870,10 @@ <h4><a href="#closure-types">5.1.8 Closure Types (Lambdas)</a></h4>
 member (static or nonstatic), inline variable, or variable template,
 it is encoded in a qualified name with a
 <code>&lt;<a href="#mangle.prefix">prefix</a>&gt;</code> of the form:
-<code><pre><font color=blue>  &lt;closure-prefix&gt; ::= [ &lt;<a href="#mangle.prefix">prefix</a>&gt; ] &lt;<i>variable or member</i> <a href="#mangle.unqualified-name">unqualified-name</a>&gt; [&lt;<a href="#mangle.template-args">template-args</a>&gt;] M
+<code><pre><font color=blue>
+    &lt;closure-prefix&gt; ::= [ &lt;<a href="#mangle.prefix">prefix</a>&gt; ] &lt;<i>variable or member</i> <a href="#mangle.unqualified-name">unqualified-name</a>&gt; M
+                     ::= &lt;<i>variable template</i> <a href="#mangle.template-prefix">template-prefix</a>&gt; &lt;<a href="#mangle.template-args">template-args</a>&gt; M
 </font></pre></code>
-where the <code>&lt;<a href="#mangle.template-args">template-args</a>&gt;</code>
-is present for a closure type within a variable template specialization
-and absent otherwise.
 For example:
 <code><pre>
 	template&lt;typename T> struct S {