symtable: Add @lparent to let lparam symbols

* src/current/include/preproc/symtable.xsl (preproc:symtable)[c:let]:
    Add @lparam to symbol.

src/current/include/preproc/symtable.xsl

@@ -836,14 +836,14 @@
 
   <!-- the name is generated automatically by the preprocessor; the user cannot
        set it -->
-  <xsl:variable name="lname" select="
-    ancestor::c:let[
-      c:values/c:value[ @name=$name ]
-    ]/@name
-  " />
+  <xsl:variable name="lname" as="xs:string?"
+                select="ancestor::c:let[1]/@name" />
 
+  <!-- @lparent instead of @parent because the let does not actually exist
+       as a symbol -->
   <preproc:sym name=":{$lname}:{@name}" local="true" varname="{@name}"
-    type="lparam" dtype="{@type}" dim="{$dim}" desc="{@desc}" tex="{@sym}" />
+    type="lparam" dtype="{@type}" dim="{$dim}" desc="{@desc}" tex="{@sym}"
+    lparent="{$lname}" />
 
   <xsl:apply-templates mode="preproc:symtable" />
 </xsl:template>

src/symtable/symbols.xsl

@@ -247,6 +247,11 @@
     defined scope (e.g. function parameters; let expressions).
   This symbol is not used by the linker.
 
+  @item lparent
+  Local parameter parent.
+  This is set for @code{let} expressions in place of @code{@@parent}
+    since the parent let does not actually generate a symbol.
+
   @item const
   Global constant.
   Constant values (of any dimension).