Default remap_path_prefix broke backtrace

[ashi009]

As shown in rust-lang/backtrace-rs#691 and rust-lang/rust#135853, the current default value used for remap_path_prefix will prevent backtrace from printing source info.

We should change it to something other than "", say ".", "/" or "__main__/" etc.

rules_rust/rust/private/rustc.bzl

Line 824 in c075460

remap_path_prefix = "",

[UebelAndre]

I'd be happy to review a pull-request making an update like this!

[rejuvenile]

I can confirm that "./" results in a clickable stack trace for sources built in my working tree. Other values might also work.