`tests/run-make-cargo/thumb-none-cortex-m` does not lock Cargo dependencies and can break

[japaric]

what the title says. the v1.4.1 release of the cc crate was broken (rust-lang/cc-rs#1844) because it invoked arm-none-eabi-gcc with a -mno-* flag which is specific to clang. v1.4.2 has fix for that bug but this test uses a version of the cortex-m crate that does not lock dependencies so Cargo transiently chose cc v1.4.1 which made the cortex-m build fail.

it would preferable to switch to a newer version of the cortex-m that includes a lockfile. the current version is v0.5.0 from 2018 which was a time when library crates including lockfiles was still not the norm.