Incorrect source file paths for inlined stdlib code

[rocallahan]

This seems related to #34179 ... CCing @luser @tromey.

I did cargo new --bin test_crate; cd test_crate; cargo build; objdump --dwarf=rawline target/debug/test_crate. The output for the first compilation unit has

 The Directory Table (offset 0x1c):
  1     libstd/sys/unix/process
  2     src

 The File Name Table (offset 0x39):
  Entry Dir     Time    Size    Name
  1     1       0       0       process_common.rs
  2     2       0       0       main.rs

If I understand #34187 correctly the intent was that the stdlib code (process_common.rs in this case) should have been given an absolute path, since test_crate/libstd/sys/unix/process/process_common.rs certainly doesn't exist. But here we are. rustc 1.31.1 (b6c32da9b 2018-12-18).

[Centril]

cc @alexcrichton

[luser]

This is probably a dupe of #54408 which was fixed in #54626 . We noticed this in Firefox crash reports as well. It should be fixed on beta.

[rocallahan]

Ah yes, it's fixed on nightly. Sorry, I should have tested that before filing. Thanks!