Using a --target value that matches rustup show causes a range of bugs.

1. Two different crates with name 'X' error only when using --target=  #3665
2. MSVC: Spurious PDB error on the bots rust#33145 (comment)

cargo 0.18.0-nightly (5db6d64 2017-03-03)
rustc 1.17.0-nightly (b1e31766d 2017-03-03)

Both target/$PROFILE/ and target/$TARGET/$PROFILE folders are populated with binaries, nearly all of which are duplicates.

Issues seem to be more common in projects with a sufficiently large dependency graph. And when compiling for windows targets.