RFE: add --debug to build and --release to install

[ensc]

With traditional build systems I am using a workflow like

make build CFLAGS='-O2 -g3'
make check
make install DESTDIR=`pwd`/i

to

1. build the software

2. run tests

3. install the built artifacts

With cargo, this is more complicated because cargo install executes the build step and ignores the previous cargo build. But build and install expect different options; e..g. you have to do either

cargo build             --feature foo
cargo install --debug   --feature foo --path . --root `pwd`/i 

or

cargo build   --release --feature foo
cargo install           --feature foo --path . --root `pwd`/i 

This require to carry around two different options expressing the same.

Things would be more easy when both --debug and --release are available to build + install. Then, you can just call

cargo build   $CARGO_FLAGS
cargo install $CARGO_FLAGS --path . --root `pwd`/i 

and use a common CARGO_FLAGS variable.

[ehuss]

I think we're moving towards using --profile=release and --profile=debug instead of adding more --release and --debug flags. It is implemented on nightly, and is tracked in #6988.

[ehuss]

Closing since we will likely be using the --profile flag.