[GHC] #9230: Make -fwarn-tabs the default

[GHC]

#9230: Make -fwarn-tabs the default
-------------------------------------+-------------------------------------
              Reporter:  dfeuer      |            Owner:  mlen
                  Type:  feature     |           Status:  new
  request                            |        Milestone:  7.10.1
              Priority:  normal      |          Version:  7.8.2
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------

Comment (by thoughtpolice):

 The above patch does all of the above correctly; it is also on Phabricator
 - see Phab:D255 (which also built correctly).

 In essence it just adds `Opt_WarnTabs` (AKA `-fwarn-tabs`) to
 `standardWarnings` in `DynFlags`, which is the correct move. Next, it
 disables `-fno-warn-tabs` when building the libraries by modifying `mk
 /validate-settings.mk` to include `-fno-warn-tabs`, so that everything can
 validate correctly.

 I need to do a review on the testsuite changes in the patch, but it seems
 fine at a quick glance (I mostly wonder about the changes to the testsuite
 driver).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9230#comment:18>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler