Support tracking: GHDL [VHDL-2008] about compliance-tests

[eine]

As commented in ghdl/ghdl#1063, most matching operators (?/=, ?<, ?<=, ?>, ?>=) are not implemented in GHDL yet but the equality operator is available.

Unfortunately, 2 of the 8 related tests in tb_matching_operator.vhd fail with the current implementation because of some weird interaction between VUnit and GHDL. A workaround, which is shown in https://github.com/VHDL/Compliance-Tests/tree/ghdl-matchingop, is to explicitly set the type of 'H' and 'W'. @LarsAsplund, what do you think? Should we ensure that the signals/variables that are compared are explicitly of type std_logic? It was "a stupid mistake" (ghdl/ghdl#1063 (comment)).