Add missing forward reference

xtldr/includes/xtldr.h

@@ -29,6 +29,10 @@ EFI_STATUS
 BlAllocateMemoryPool(IN UINT_PTR Size,
                      OUT PVOID *Memory);
 
+XTCDECL
+EFI_STATUS
+BlBuildPageMap(IN PXTBL_PAGE_MAPPING PageMap);
+
 XTCDECL
 VOID
 BlClearConsoleLine(IN ULONGLONG LineNo);