Link problem with latest mingw and uuid

[TheJare]

Apparently they have been aware of a problem with their uuid libraries for months, but latest version from March still fails. Fix was trivial in the wx/setup_windows_amd64.go (and wx/setup_windows_386.go I suppose), add the "--allow-multiple-definition" flag to the existing -Wl LDFLAG in line 5 so it looks like:

-Wl,--subsystem,windows,--allow-multiple-definition

As this is a workaround to their problem, I'm not submitting a pull request but leaving this here to inform others.

[qindj]

@TheJare Thanks for the workaround!

To inform others, Author has added this workaround, see https://github.com/dontpanic92/wxGo/wiki/Available-Go-Tags