Migrate build system to CMake

See #5895 for details.

This commit does not include CI or documentation changes.

frontends/ast/CMakeLists.txt

@@ -0,0 +1,13 @@
+yosys_core(ast
+	ast_binding.cc
+	ast_binding.h
+	ast.cc
+	ast.h
+	dpicall.cc
+	genrtlil.cc
+	simplify.cc
+	LIBRARIES
+		$<${YOSYS_ENABLE_LIBFFI}:${Dlfcn_LIBRARIES};PkgConfig::libffi>
+	REQUIRES
+		sha1
+)