…ble builds

(cherry picked from commit 56e11bc)

By overriding each dependency on every level of the dependency tree we
are creating a lot of unnecessary instances of the same derivation

Looking at the output size of `nix-instantiate --trace-function-calls
-vvvv …` and the execution time I got about a 10x improvement after
applying this change.

It was probably good intentions that lead to these overrides but in
practice no tooling (that I know of) really needs this. `carnix` and
`crate2nix` are fine without those overrides. Furthermore I believe that
it is the job of the tooling around `buildRustCrate` to provide a
coherent set of overrides. By not enforcing all of the overrides, debug
flags, verbosity, … to be the same throughout the closure we also allow
consumers to override specific aspects of the crates. Some (older?)
crates might need different `crateOverrides` then newer crates with the
same name. Currently such situations can not (easily) be implemented
with the override in-place.

(cherry picked from commit be5597f)

* Make errors include the crate name and make them much more prominent.
* Move more code into lib.sh
* Already source generated logging code and lib.sh in configure

(cherry picked from commit 04e7462)

…sub directories

This is what cargo does for git repositories.

See related issues:

* nix-community/crate2nix#53
* nix-community/crate2nix#33

(cherry picked from commit 8a6638d)

According to the Cargo documentation:

> The build script does not have access to the dependencies listed in
> the dependencies or dev-dependencies section (they’re not built
> yet!). Also, build dependencies are not available to the package
> itself unless also explicitly added in the [dependencies] table.

https://doc.rust-lang.org/cargo/reference/build-scripts.html

This change separates linkage of regular dependencies and build
dependencies.

(cherry picked from commit ea6e048)

(cherry picked from commit 412c72d)

This is a slight readability boost, I think.

(cherry picked from commit 7533876)

Linkage order is significant and sorting can result in link errors.

(cherry picked from commit d8b8537)

(cherry picked from commit 2f7fb1c)

As it turns out Darwin does most of the things differently then "normal"
systems. They are using a different shared library extension and require
an obscure commandline parameter that has to be added to every build
system out there. That issue seems to be with clang on Darwin as on
Linux that flag isn't required to build the very same tests (when using
clang).

After adjusting these two details the tests are running fine on the
darwin box that I was able to obtain.

(cherry picked from commit c8de31b)

...and remove superfluous dependency files (*.d).
...and copy dSYM directories on Mac OS when in release=false mode.

(cherry picked from commit 782b304)

[20.03] buildRustCrate fixes backports