Rollup merge of #119637 - aoli-al:master, r=cuviper

Pass LLVM error message back to pass wrapper.

When rustc fails to load a plugin, it should provide more detailed error message. Before this PR, rustc prints:

```
error: failed to run LLVM passes: Failed to load pass pluginPLUGIN_NAME.so
```

This PR passes LLVM errors back to rustc. After this PR, rustc prints:

```
error: failed to run LLVM passes: Could not load library 'PLUGIN_NAME.so': PLUGIN_NAME.so: undefined symbol: _ZN4llvm9DebugFlagE
```

This PR only contains usability improvements and does not change any functionality. Thus, no new unit test is implemented.

Author: matthiaskrgr