Also check structs with a single element of varying types when searching for a type with a particular alignment.

[SVN r19908]

libs/type_traits

@@ -1 +1 @@
-Subproject commit 42f271a4dc3f4bce7de8bb2154b19016d4b89cf9
+Subproject commit 2ffc663dd5c778c5a2e847e91b32dc87c40143e3