Prefer bundled linker redux

[vadimcn]

Based on Windows bundle feedback we got to date,

• We do want to prefer the bundled linker: The external one might be for the wrong architecture (e.g. 32 bit vs 64 bit). On the other hand, binutils don't add many new features these days, so using an older bundled linker is not likely to be a problem.
• We do want to prefer bundled libraries: The external ones might not have the symbols we expect (e.g. what's needed for DWARF exceptions vs SjLj). Since -L rustlib/<triple>/lib appears first on the linker command line, it's a good place to keep our platform libs that we want to be found first.

Closes #18325, closes #17726.

[alexcrichton]

Did you move the bundled libraries from under gcc to back under bin to pass fewer -L flags? I would think that for organizational purposes it would be nice to keep them separated. Other than that though, this looks great to me, thanks!

[brson]

I'm also happy with this as long as @alexcrichton is satisfied he can get cargo linking correctly under this scheme.

[alexcrichton]

Not entirely sure how we'll manage it, but I'm sure I can think of something for Cargo!

[vadimcn]

@alexcrichton, I am trying to keep this all sufficiently generic so that we don't need to add Windows-specific if's in rustc code. Especially now, that "Flexible Target Specifications" has landed.

rustlib/<triple>/gcc/lib feels awfully Windows-specific. I suppose we could have rustlib/<triple>/lib for Rust libs and rustlib/<triple>/lib/native for platform-specific stuff... Any sugggestions?

cc @cmr

[jeffnyman]

I made a comment in #17726 (which I know is closed) and that issue redirects people to this one. I find the error in that previous issue still happens as of right now with a complete up-to-date install of Rust via rustup.

Specifically, I see the following error when trying to compile a basic Rust program on Windows:

collect2.exe: error: ld returned 1 exit status

And it's clear that the Rust toolchain is using an existing mingw32 setup, not it's bundled one. I'm using the following:

stable-x86_64-pc-windows-gnu (default)
rustc 1.57.0 (f1edd0429 2021-11-29)

I did try adding the the following to the PATH:

.rust\toolchains\stable-x86_64-pc-windows-gnu\lib\rustlib\x86_64-pc-windows-gnu\bin\gcc-ld

I added that before the part of the PATH that had a link to the bin directory of the mingw setup. The only way I found this could work was to entirely remove the reference to mingw path from the setup entirely. And when I did that, I didn't even need the above path to the toolchains in place.

So is that the solution that was decided upon?