Auto merge of #57018 - dcreager:redundant-linker, r=alexcrichton

Keep last redundant linker flag, not first

When a library (L1) is passed to the linker multiple times, this is sometimes purposeful: there might be several other libraries in the linker command (L2 and L3) that all depend on L1.  You'd end up with a (simplified) linker command that looks like:

```
-l2 -l1 -l3 -l1
```

With the previous behavior, when rustc encountered a redundant library, it would keep the first instance, and remove the later ones, resulting in:

```
-l2 -l1 -l3
```

This can cause a linker error, because on some platforms (e.g. Linux), the linker will only include symbols from L1 that are needed *at the point it's referenced in the command line*.  So if L3 depends on additional symbols from L1, which aren't needed by L2, the linker won't know to include them, and you'll end up with "undefined symbols" errors.

A better behavior is to keep the *last* instance of the library:

```
-l2 -l3 -l1
```

This ensures that all "downstream" libraries have been included in the linker command before the "upstream" library is referenced.

Fixes rust-lang#47989

0 files changed, 0 insertions, 0 deletions