Improve test coverage - multiple GDBs and Platforms

There are some tests and functionality that are GDB version dependent. Like we have with DSF-GDB we should be running tests against all supported GDB versions. At the moment the whole testsuite takes only a few minutes to run - so adding all the supported GDB versions should not be too cumbersome. I don't recommend we change how much `yarn test` does, but instead add a new longer test.

- [ ] Is there a standard way to enable long running tests with yarn/mocha?
- [ ] provide way to specify which gdb version to use (this is partially there already with `--gdb-path`, but you can't today do `yarn test --gdb-path gdb.x.y` because the --gdb-path is not passed to each inferior test suite.
- [ ] add windows testing support - this is dependent on cdt-infra changes, see [WIP](https://github.com/eclipse-cdt/cdt-infra/tree/jonah/windows_build)
- [ ] ?? Add cross compilation test - probably use [qemu arm](https://wiki.qemu.org/Documentation/Platforms/ARM) and cross compilation toolchain (can we use what is in Ubuntu packages?)