[WIP] [NeedsAcceptOrRejectFromWalter] Remove hardcoded phobos info from the compiler

[marler8997]

This PR is going to take some coordination between dmd/druntime/phobos and also the packaging tools. The basic idea is to move all the hard-coded information about the standard library into dmd.conf. This puts the responsibility of configuring phobos on the components who install/package dmd rather than hard-coding that configuration into DMD.

For now I've simply removed all the hard-coded information about phobos to see what breaks. In theory, this PR should be able to be pushed as-is once the other tools are enhanced to take on the role of configuring phobos away from the compiler.

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[WalterBright]

Since the default library names can be overridden from the command line, why is this necessary?

[marler8997]

Since the default library names can be overridden from the command line, why is this necessary?

I wouldn't say it's necessary. What it does is provide separation between the compiler and the standard library. Today you can override/disable the default library, but because there's no clear separation, we've mistakenly introduced default library "isms" into EVERY compilation.

On Windows DMD hardcodes user32 and kernel32 as a dependency to every program, even when defaultlib and conf are disabled:

https://github.com/dlang/dmd/blob/master/src/dmd/link.d#L295

And on posix DMD does the same thing, it always adds -lpthread, -lm, and on linux also adds -lrt and -ldl, even when defaultlib and conf are disabled:

https://github.com/dlang/dmd/blob/master/src/dmd/link.d#L672

These 2 issuecan be fixed (see #9831), but this PR helps keep them fixed. The compiler doesn't need to hard-code any information about the standard library, by removing it, it helps issues like this from happening again.

But if you don't see any value with that, I'm fine with closing and just fixing the immediate issues. Fixing those issues is all I "need", this is more of an optional addition that I think will help keep those issues from happening again. Let me know if you think this PR is justified or not.

[marler8997]

Cleaning up old PRs that aren't going anywhere.