Make out of tree build testing possible

tests/functional/test_functional.py

@@ -1,6 +1,6 @@
 import subprocess
 import pytest
-import sys
+import os
 import shlex
 from pathlib import Path
 
@@ -18,7 +18,7 @@ def run(cmd, **kwargs):
     assert status.returncode == 0, f"{cmd[0]} failed"
 
 def yosys(script):
-    run([base_path / 'yosys', '-Q', '-p', script])
+    run([os.environ.get("YOSYS", "../../yosys"), '-Q', '-p', script])
 
 def compile_cpp(in_path, out_path, args):
     run(['g++', '-g', '-std=c++20'] + args + [str(in_path), '-o', str(out_path)])
@@ -35,7 +35,7 @@ def yosys_sim(rtlil_file, vcd_reference_file, vcd_out_file, preprocessing = ""):
         # since yosys sim aborts on simulation mismatch to generate vcd output
         # we have to re-run with a different set of flags
         # on this run we ignore output and return code, we just want a best-effort attempt to get a vcd
-        subprocess.run([base_path / 'yosys', '-Q', '-p',
+        subprocess.run([os.environ.get("YOSYS", "../../yosys"), '-Q', '-p',
             f'read_rtlil {quote(rtlil_file)}; sim -vcd {quote(vcd_out_file)} -a -r {quote(vcd_reference_file)} -scope gold -timescale 1us -fst-noinit'],
             capture_output=True, check=False)
         raise