remap-debuginfo causes some rustc tests to fail

[ehuss]

Setting remap-debuginfo to true in config.toml will cause a few tests to fail. They are:

• ui/impl-trait/impl-generic-mismatch.rs
• ui/consts/const-size_of-cycle.rs
• ui/type_length_limit.rs

The issue is that these tests use $SRC_DIR in their .stderr output, but when the standard library is built with --remap-path-prefix, these paths will not be shown at all in the output.

I can't think of an easy way to work around that. My only idea is to add an "ignore" flag to compiletest so that these tests can be ignored when remapping is enabled.

[ehuss]

I believe this is now resolved, probably via #70642 (or one of its related PRs).