Add build specification item verification

[Sebastian Huber]

The new build system uses build specification items to define what is built and how it is built. Add a ./waf --rtems-verify-spec option to verify that the build specification items are sane. For example, check that there are no cycles in the graph, all required attributes are present, the attribute values have the proper type, no additional attributes are present, all UIDs are resolvable, etc.

[Sebastian Huber]

The basic functionality for a verification of build items is implemented in the RTEMS Qualification Tools repository:

​https://git.rtems.org/sebh/rtems-qual.git/tree/specverify.py

To make use of it, one option would be to install the RTEMS Qualification Tools Python modules under ${prefix}/share/rtems parallel to the rtemstoolkit modules. Only if the wscript should do the verification, then the module is loaded.

Missing features are:

• verify that the directed graph of specification items has no cycles (depending on the link role)

• specify and verify required links, roles, and target types for item types

• detect isolated items

• add warning conditions

• improve the output of failed assertions