Fix JuliaLang#7854

- label `comprehensions`
- add cross-reference in section about scoping in for loops and
  comprehensions

doc/manual/arrays.rst

@@ -139,6 +139,8 @@ Expression Yields
 Note that this form does not do any concatenation; each argument becomes
 an element of the resulting array.
 
+.. _comprehensions:
+
 Comprehensions
 --------------
 

doc/manual/variables-and-scoping.rst

@@ -268,10 +268,10 @@ is a different variable than the outer local ``x``.
 For Loops and Comprehensions
 ----------------------------
 
-For loops and comprehensions have a special additional behavior: any
-new variables introduced in their body scopes are freshly allocated for
-each loop iteration. Therefore these constructs are similar to ``while``
-loops with ``let`` blocks inside::
+``for`` loops and :ref:`comprehensions <comprehensions>` have a special
+additional behavior: any new variables introduced in their body scopes are
+freshly allocated for each loop iteration. Therefore these constructs are
+similar to ``while`` loops with ``let`` blocks inside::
 
  Fs = cell(2)
  for i = 1:2