+ enable WebAssembly threads with the internal linker (which still doesn't work

  with threads) if FPC is compiled with the FPC_WASM_THREADS_INTERNAL_LINKER
  define

compiler/options.pas

@@ -2246,12 +2246,14 @@ begin
       StopOptions(1);
     end;
 
+{$ifndef FPC_WASM_THREADS_INTERNAL_LINKER}
   if (ts_wasm_threads in init_settings.targetswitches) and
      not (cs_link_extern in init_settings.globalswitches) then
     begin
       Message(option_wasm_threads_require_external_linker);
       include(init_settings.globalswitches,cs_link_extern);
     end;
+{$endif FPC_WASM_THREADS_INTERNAL_LINKER}
 {$endif}
 
 {$ifdef i8086}