[GHC] #9713: Update comment about C helper for dynamic exports.

[GHC]

#9713: Update comment about C helper for dynamic exports.
-------------------------------------+-------------------------------------
              Reporter:  int-e       |            Owner:
                  Type:  task        |           Status:  patch
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Easy (less than 1
       Type of failure:  Other       |  hour)
             Test Case:              |       Blocked By:
              Blocking:              |  Related Tickets:
Differential Revisions:              |
-------------------------------------+-------------------------------------

Comment (by thomie):

 No knowing anything about this code, I have the following
 questions/remarks, mostly about the commit message:
 * Please mention the Trac number.
 * Patch does more than update a comment, needs better title.
 * What does it mean that f_helper is a helper in C "approximately"?
 * In which commit did the RTS API change?
 * Are there other calls to rts_evalIO anywhere that need updating?
 * Why did this not get caught by a test? Should one be added?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9713#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler