Fixing issues, enabled warnings and fixing on linux

src/test/tests.cpp

@@ -26,6 +26,7 @@ void Wait(mco_coro *co) {
 }
 
 void PlayTestOpen(mco_coro *co) {
+    Unused(co);
     // Open file, move a little, then open again and verify the caret didn't move
     // String basic_env_cpp = Format(SysAllocator, "%S/test_env", TestDir);