fix CMake build on macOS

CMakeLists.txt

@@ -253,6 +253,9 @@ if(WIN32)
   add_compile_definitions(WIN32_LEAN_AND_MEAN)
 endif()
 
+# Ensure dynamic library extension is always .so
+set(CMAKE_SHARED_LIBRARY_SUFFIX ".so")
+
 # Put source code here, files that are generated at build time in
 # surelog_generated_SRC
 set(synlig_SRC
@@ -291,6 +294,13 @@ set_target_properties(
 set_target_properties(synlig PROPERTIES OUTPUT_NAME "systemverilog")
 set_target_properties(synlig PROPERTIES PREFIX "")
 
+# Allow undefined symbols at link time on macOS. These symbols should already be
+# present within yosys when the plugin is loaded.
+if(APPLE)
+  set_target_properties(synlig PROPERTIES LINK_FLAGS
+                                          "-undefined dynamic_lookup")
+endif()
+
 target_include_directories(
   synlig
   PUBLIC $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/frontends/systemverilog/>