move rpath to frontend and remove native paths from it

[Jan200101]

As discussed at compiler meeting 2023-10-26.

Needed tests:

• system deps
• NixOS
• local deps

[andrewrk]

This had conflicts with master branch, but it had already passed the CI before that, so I rebased it on your behalf.

I also dropped these commits from it:

• f306d2a
• d4328e4

I don't think the build script should be doing those things. Let's discuss those changes in a follow-up if you still want to pursue those.

One more thing: With just that NativePaths one-line change you made, it looks like it might be possible to change the default of each-lib-rpath to be off, or even have that option removed altogether.

[Jan200101]

This had conflicts with master branch, but it had already passed the CI before that, so I rebased it on your behalf.

Thanks

I also dropped these commits from it:

* [f306d2a](https://github.com/ziglang/zig/commit/f306d2acdaefbf2db82c018e58a3dfbf49d321d2)

* [d4328e4](https://github.com/ziglang/zig/commit/d4328e42f4c4eede8ef93125ea1a59890b71d2c6)

I don't think the build script should be doing those things. Let's discuss those changes in a follow-up if you still want to pursue those.

These were mainly there to simplify testing the result of all the different environments without changing the overall behavior of Zig...

One more thing: With just that NativePaths one-line change you made, it looks like it might be possible to change the default of each-lib-rpath to be off, or even have that option removed altogether.

It should be able to cover NixOS and systemwide libraries, but I am unsure if it would cover user libraries. Will need to do testing before that proposal can be made.