fix quoting in win64.mak: add them only when invoking command

[rainers]

not when setting variable. This avoids having to skillfully quote variables with spaces in them: use "CC=%cl64%" instead of "CC=\"%cl64%\""

Not sure how the existing misquoting was supposed to work. Using quotes with the command is agnostic to using / instead of \ as a path separator, too.

See also dlang/druntime#2438

[dlang-bot]

Thanks for your pull request, @rainers!

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Testing this PR locally

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dub fetch digger
dub run digger -- build "master + phobos#6825"

[rainers]

Now also quoting $(MAKE)

[PetarKirov]

It looks like https://github.com/braddr/at-client/blob/master/src/diff-phobos-win64.diff needs to be updated. Or even better - removed entirely ;)

[wilzbach]

CC @braddr

[rainers]

Or even better - removed entirely ;)

braddr/at-client#10

[rainers]

With the diffs removed from the autotester, this should be unblocked.

[kinke]

This avoids having to skillfully quote variables

Lol, one way to put it. ;)

[wilzbach]

Looks like the patching is still done by the Auto-Tester:

https://auto-tester.puremagic.com/show-run.ghtml?projectid=1&runid=3546293&isPull=true