New Build System Status

[Sebastian Huber]

Hello,

I sent the documentation of the new build system some days ago and at 
least Gedare Bloom reviewed it.

https://ftp.rtems.org/pub/rtems/people/sebh/user.pdf

https://ftp.rtems.org/pub/rtems/people/sebh/eng.pdf

I rebased the build system branch to the current master and squashed all commits:

https://git.rtems.org/sebh/rtems.git/log/?h=build-2

I started the development nearly one year ago and it was basically production ready in November last year. In the mean time Hesham Almatary added basic support for clang to it. Doorstop is no longer used. This simplified the YAML files a bit since no requirements related attributes are present in the build item files. The item links are now an ordered list. This simplified the build dependencies. The item paths are now also shorter since there is no longer a duplication of the directory path in the file name.

Each build item has a license and a copyright statement list. I didn't add copyright statements for the BSP option descriptions. If someone thinks there is a statement missing or the licensing conditions are not acceptable, we can add/change it later.

I built all BSPs with all tests enabled today using the latest RTEMS 5 tool chain which is based on GCC 10. I had to disable the fenv test since the ARM support is currently broken.

The build system is ready to be merged from my point of view.