[MacPorts] #40174: upgrade mingw and add win64 cross-compiler

[MacPorts]

#40174: upgrade mingw and add win64 cross-compiler
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  Reporter:  sam.halliday@…    |      Owner:  landonf@…
      Type:  enhancement       |     Status:  new
  Priority:  Normal            |  Milestone:
 Component:  ports             |    Version:
Resolution:                    |   Keywords:
      Port:  i386-mingw32-gcc  |
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Comment (by sam.halliday@…):

 workaround is to download the mingw64 binaries for i686-darwin from
 sourceforge.

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Ticket URL: <https://trac.macports.org/ticket/40174#comment:4>
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