This commit fixes a bug accidentally introduced in #285 where some
lingering references remained to `#[cfg(thumbv6m)]` but this, since the
historical revert, was renamed to `#[cfg(thumb_1)]`. This caused on the
thumbv6m platform for the intrinsics to be accidentally omitted because
the build script didn't actually compile them but the Rust code thought
the C code was in use.
After correcting the `#[cfg]` statements the CI configuration for the
`thumb*` family of targets was all updated. The support for xargo
testing was removed from `run.sh` since it had long since bitrotted, and
the script was updated to simply build the intrinsics example to attempt
to link for each of these targets. This in turn exposed the bug locally
and allowed to confirm a fix once the `#[cfg]` statements were
corrected.
cc rust-lang/rust#60782
- add #[no_mangle] to the panic_fmt lang item to adjust to changes in
the visibility algorithm
- adjust to changes in the layout of Cargo's target directory
- use a newer Xargo to reduce the build time of the sysroot (only core
is compiled as part of the sysroot now)
this version uses the rust-src component that rustup installs instead
of fetching the source tarball from static.r-l.o, which sometimes went
wrong due to the fallible logic that Xargo 0.1.x used
`apt update` and `apt install` should be in the same Docker RUN statement, otherwise `apt update` will be cached and `apt install` will 404 if a package no longer exists.
notable changes in the docker-based testing infrastructure
- the docker containers can now modify $CARGO_HOME, to re-use the outer
Cargo registry, and the target directory to re-use build artifacts.
- the docker containers are removed when their execution finishes
because it's no longer necessary to re-start them to inspect them
because all the interesting output is in the outer target directory
