[Explorer|Shell32] Fix Build

Missed a file. See CORE-14439.

sdk/include/reactos/undocshell.h

@@ -690,6 +690,11 @@ BOOL WINAPI GUIDFromStringW(
 #define TRAYCMD_SEARCH_FILES        41093
 #define TRAYCMD_SEARCH_COMPUTERS    41094
 
+// Explorer Tray Application Bar Data Message Commands
+#define TABDMC_APPBAR     0
+#define TABDMC_NOTIFY     1
+#define TABDMC_LOADINPROC 2
+
 void WINAPI ShellDDEInit(BOOL bInit);
 DWORD WINAPI WinList_Init(void);