[GHC] #10726: Upgrade MingW-w64 distributions for windows

[GHC]

#10726: Upgrade MingW-w64 distributions for windows
-------------------------------------+-------------------------------------
              Reporter:  Phyx-       |             Owner:  Phyx-
                  Type:  task        |            Status:  new
              Priority:  normal      |         Milestone:  7.12.1
             Component:  Build       |           Version:  7.11
  System                             |
              Keywords:              |  Operating System:  Windows
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:  #9218 #9014
Differential Revisions:              |  #10435
-------------------------------------+-------------------------------------
 This is the second part of splitting up #9218.

 The goal is to move `GHC x86` from `MingW` to `MingW-w64` and to upgrade
 both the `x86` and the `x86_64` toolchains shipped with `GHC` to newer
 versions.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10726>
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