Rename {DMD,DRUNTIME,PHOBOS,VERSION}_STABLE -> _LATEST

[wilzbach]

CC @MartinNowak @CyberShadow (follow-up to #1684)

[CyberShadow]

Why? Are all these renames achieving something?

[wilzbach]

Cleaning up the Makefile or in Martin's words:

Those should be named {DMD,DRUNTIME,PHOBOS}_LATEST, as they are a specific version, but not intended to be used as stable tool compiler.
In particular confusing since we have a STABLE_DMD_VER in that same makefile.

[CyberShadow]

OK, deferring to Martin then

[MartinNowak]

Why? Are all these renames achieving something?

Yes, we want to introduce a new target named release for the installer builds, and use the correct term latest for the current one.
Also the term stable has 2 meanings in the current Makefile.

[dlang-bot]

Thanks for your pull request, @wilzbach!

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[wilzbach]

Rebased to the latest, greatest posix.mak. I am assuming that Martin needs to update his diff, so it probably make sense to wait for him here.

[wilzbach]

Rebased and this should be good to go now.
IIRC the nightly build server doesn't build the dlang.org anymore, so there's no risk at breaking it again.

[CyberShadow]

Build is failing.

[MartinNowak]

Why? Are all these renames achieving something?

Clarifying terminology, the makefile is quite a mess atm.