Migrate build system to CMake

See #5895 for details.

This commit does not include CI or documentation changes.

pyosys/modinit.py

@@ -0,0 +1,19 @@
+import os
+import sys
+
+sys.setdlopenflags(os.RTLD_NOW | os.RTLD_GLOBAL)
+
+__dir__ = os.path.abspath(os.path.dirname(__file__))
+sys._pyosys_dir = os.path.abspath(__dir__)
+
+bin_ext = ".exe" if os.name == "nt" else ""
+
+_share_candidate = os.path.join(__dir__, "share")
+if os.path.isdir(_share_candidate):
+    sys._pyosys_share_dirname = _share_candidate + os.path.sep
+
+_abc_candidate = os.path.join(__dir__, f"yosys-abc{bin_ext}")
+if os.path.isfile(_abc_candidate):
+    sys._pyosys_abc = _abc_candidate
+
+__all__ = ["libyosys"]