[fix] fix the build command for symbiyosys

[Henkru]

The current run step of the symbiyosys backend generates a sby command which includes the hardcoded -d build argument. However, this command line argument is incompatible with multiple tasks (see #257).

If the -d build argument is specified, the output folder of sby is forced to build/<core>/<target>-symbiyosys/build. Otherwise, the following path is used: build/<core>/<target>-symbiyosys/test_<taskname>.

This fix removes the hardcoded -d argument and introduces a new extra_options tool option for the symbiyosys backend, which can be used to pass additional arguments for the sby command (e.g. -d build, if necessary).

The example usage of the extra_options:

   symbiyosys:
     tasknames:
       # A list of task names to pass to sby. Defaults to empty (in which case
       # sby will run each task in the .sby file)
       - my_proof
     extra_options:
       # A list of extra command line arguments to sby. Defaults to empty.
       - -d
       - build

Closes #257.

[olofk]

Thanks. This sounds good to me. Hard coded parameters should be avoided as far as possible. I would like to rename extra_options to sby_options for symmetry with other tools.