Temporarily export _BITMASK_OPS for __std_fs_file_attr (#3331)

stl/inc/xfilesystem_abi.h

@@ -79,7 +79,11 @@ enum class __std_fs_file_attr : unsigned long {
 };
 _END_EXTERN_C
 
+#if 1 // TRANSITION, DevCom-10247495
+_BITMASK_OPS(_EXPORT_STD, __std_fs_file_attr)
+#else // ^^^ workaround / no workaround vvv
 _BITMASK_OPS(_EMPTY_ARGUMENT, __std_fs_file_attr)
+#endif // ^^^ no workaround ^^^
 
 _EXTERN_C
 enum class __std_fs_reparse_tag : unsigned long {