Running rustup installs then removes rustc installation

[huonw]

The switch to the new installers seems to result in rustup.sh deleting the rustc. It downloads and installs rustc fine, then downloads cargo, but the installer for that first deletes rustc as legacy, and then installs cargo, meaning cargo works fine... but there's no compiler.

Snippet of output at the end of installing rustc/beginning of installing cargo.

...
install: installing /usr/local/share/man/man1/rustc.1
install: installing /usr/local/share/man/man1/rustdoc.1
install: 
install: verifying installed binaries are executable

    Rust is ready to roll.

rustup: Extracting cargo-nightly-x86_64-unknown-linux-gnu.tar.gz
install: looking for install programs
install: 
install: found mkdir
install: found printf
install: found cut
install: found grep
install: found uname
install: found tr
install: found sed
install: 
install: processing ./rustup-tmp-install/cargo-nightly-x86_64-unknown-linux-gnu/install.sh args
install: 
install: CFG_DESTDIR          :=  
install: CFG_PREFIX           := /usr/local 
install: CFG_LIBDIR           := /usr/local/lib 
install: CFG_MANDIR           := /usr/local/share/man 
install: 
install: validating ./rustup-tmp-install/cargo-nightly-x86_64-unknown-linux-gnu/install.sh args
install: 
install: verifying platform can run binaries
install: verifying destination is writable
install: verifying destination is not the same as source
install: removing legacy file /usr/local/bin/rust-lldb
install: removing legacy file /usr/local/bin/rustc
install: removing legacy file /usr/local/bin/rustdoc
install: removing legacy file /usr/local/lib/libarena-4e7c5e5c.so
install: removing legacy file /usr/local/lib/libflate-4e7c5e5c.so
install: removing legacy file /usr/local/lib/libfmt_macros-4e7c5e5c.so
...

cc @brson

[steveklabnik]

Tons and tons of IRC people hitting this today.

[Binero]

Duplicate of #20364

[alexcrichton]

Closing as a dupe of #20364