Make cargo as relative symlink not absolute (#6780)
Make cargo as relative symlink not absolute (#6780)

This makes the .cache/pants/rust directory more self-contained and copyable
tdyas/pants,wisechengyi/pants,twitter/pants,tdyas/pants,benjyw/pants,wisechengyi/pants,tdyas/pants,pantsbuild/pants,benjyw/pants,tdyas/pants,twitter/pants,twitter/pants,twitter/pants,pantsbuild/pants,jsirois/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants,tdyas/pants,twitter/pants,wisechengyi/pants,twitter/pants,jsirois/pants,jsirois/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,benjyw/pants,tdyas/pants,tdyas/pants,twitter/pants,twitter/pants,tdyas/pants,tdyas/pants,wisechengyi/pants,pantsbuild/pants,wisechengyi/pants,pantsbuild/pants,benjyw/pants,wisechengyi/pants,twitter/pants,wisechengyi/pants,wisechengyi/pants,wisechengyi/pants