[GHC] #12485: -package-db flags now need to be sorted by dependency order

[GHC]

#12485: -package-db flags now need to be sorted by dependency order
-------------------------------------+-------------------------------------
           Reporter:  niteria        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Package        |           Version:  8.0.1
  system                             |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 After 39b71e81ec1044518f065d0055676d713521e483 putting the -package-db
 flags in the wrong order will result in a compile error:
 {{{
 <command line>: cannot satisfy -package-id b-1-XXX:
     b-1-XXX is unusable due to missing or recursive dependencies:
       a-1-XXX
     (use -v for more information)
 }}}

 See attached file for a repro.

 It's reproduces in 8.0.1 and HEAD. Doesn't reproduce in GHC 7.10.3 or
 after reverting the above mentioned commit.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12485>
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