install: Verify that installed compiler runs

Another sanity check. Can be disabled in `install.sh` via `--disable-verify`
and `configure` with `--disable-verify-install`.
install: Explicitly delete the manifest during uninstall. Misc cleanup
install: Fix string formatting in an error
install: Extract function for creating absolute paths and reuse it
install: More error handling
mk: Restore DESTDIR
auto merge of #13187 : brson/rust/dist, r=alexcrichton