GHDL not setting cwd correctly

[sigmuha]

Version: 4.7.0
When simulating GHDL couldn't read a test.bin with a relative path, even though it was located under vunit_out/ghdl/test.bin. This worked correctly when using modelsim/questa. It seems as the GHDL simulator was not running under the correct directory. I traced the bug to GHDL's simulate method, where I replaced line 390 in vunit/sim_if/ghdl.py

proc = Process(cmd, env=gcov_env)

with

proc = Process(cmd, cwd=self.output_path, env=gcov_env)

Which is more similar to how modelsim/questa is run. I believe NVC also has the same bug in vunit/sim_if/nvc.py:

proc = Process(cmd)