Path remapping: Make behavior of diagnostics output dependent on presence of --remap-path-prefix.
Path remapping: Make behavior of diagnostics output dependent on presence of --remap-path-prefix.

graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust