* include/std/type_traits (is_aggregate, is_aggregate_v): New.
* testsuite/20_util/is_aggregate/requirements/explicit_instantiation.cc:
New.
* testsuite/20_util/is_aggregate/requirements/typedefs.cc: Likewise.
* testsuite/20_util/is_aggregate/value.cc: Likewise.

From-SVN: r246651