Cleanup headers

Source/OS/dn_os.h

@@ -1,8 +1,10 @@
 #if !defined(DN_OS_H)
 #define DN_OS_H
 
-#include "../dn_base_inc.h"
-#include "../dn_os_inc.h"
+#if defined(_CLANGD)
+  #include "../dn_base_inc.h"
+  #include "../dn_os_inc.h"
+#endif
 
 #include <new> // operator new
 
@@ -33,6 +35,8 @@
   #include <emscripten/fetch.h> // emscripten_fetch (for DN_OSHttpResponse)
 #endif
 
+extern DN_CPUFeatureDecl g_dn_cpu_feature_decl[DN_CPUFeature_Count];
+
 // NOTE: DN_OSDate /////////////////////////////////////////////////////////////////////////////////
 struct DN_OSDateTimeStr8
 {