Prefer 64 bit over 32 bit DMD on Windows 64 bit.

[veelo]

Fixes https://issues.dlang.org/show_bug.cgi?id=23623

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	23623	minor	On 64 bit Windows the path should point to 64 bit dmd.

[veelo]

I haven't built the installer at home, I am hoping CI will give me one to confirm that this actually works...

[thewilsonator]

Please title the commit message to say "Fix issue 223623: ..."

[veelo]

Thanks guys.