The patch to migrate to mingw-w64 / gcc 4.8.3 is finally starting to look reasonable (Phab:D339). Whew!
The part about downloading the tarball was relatively straightforward, but the mingw migration has been really tricky, in part due to the gcc version bump, but mostly, I think, due to use of mingw-w64 on i686 as well (which is a supported configuration). In particular, "#define _MSVCRT_ 1" took ages to figure out after digging through heaps of headers and weird errors. I am not sure I would have signed on if I had an idea of how much effort this needed... Jeez.
On the bright side, now that we have standartised on mingw-w64, further gcc version upgrades should be relatively straightforward.
Could people with some experience in Windows matters take a look at the patch? In particular, rts/Linker.c has been a problem; my fixes there seem to work but I have no idea if the approach is right (the whole file does seem like a grabbag of ad-hocness though).
The patch also could use some more testing (both for x86 and for x86-64). There are still some validate.sh failures (although I am actually seeing fewer than with the legacy setup), some of which could probably be fixed easily. Some additional eyes and fingers on keyboards would be very welcome there.
If you want to experiment with the patch, make sure to also patch in the related changes listed in the last comment on the Phab page.
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Gintautas Miliauskas