Auto merge of #83846 - torhovland:issue-10971, r=davidtwco

Auto merge of #83846 - torhovland:issue-10971, r=davidtwco

Added the --temps-dir option

Fixes #10971.

The new `--temps-dir` option puts intermediate files in a user-specified directory. This provides a fix for the issue where parallel invocations of rustc would overwrite each other's intermediate files.

No files are kept in the intermediate directory unless `-C save-temps=yes`.

If additional files are specifically requested using `--emit asm,llvm-bc,llvm-ir,obj,metadata,link,dep-info,mir`, these will be put in the output directory rather than the intermediate directory.

This is a backward-compatible change, i.e. if `--temps-dir` is not specified, the behavior is the same as before.