PR libstdc++/81468 constrain std::chrono::time_point constructor
PR libstdc++/81468
* include/std/chrono (__enable_if_is_duration)
(__disable_if_is_duration): New alias templates to simplify SFINAE.
(duration_cast, floor, ceil): Use __enable_if_is_duration.
(duration::__is_float, duration::__is_harmonic): New alias templates
to simplify SFINAE.
(duration::duration(const _Rep2&)): Use _Require, __is_float and
__is_harmonic.
(duration::duration(const duration<_Rep2, _Period2>&)): Likewise.
(__common_rep_type): Remove, replace with ...
(__common_rep_t): New alias template.
(operator*, operator/, operator%): Use __common_rep_t and
__disable_if_is_duration.
(time_point::time_point(const time_point<clock, _Dur2>&)): Add missing
constraint from LWG DR 1177.
* testsuite/20_util/duration/cons/dr1177.cc: New.
* testsuite/20_util/duration/literals/range.cc: Update dg-error line.
* testsuite/20_util/duration/requirements/typedefs_neg1.cc: Likewise.
* testsuite/20_util/duration/requirements/typedefs_neg2.cc: Likewise.
* testsuite/20_util/duration/requirements/typedefs_neg3.cc: Likewise.
* testsuite/20_util/time_point/cons/81468.cc: New.
From-SVN: r252085
d0dda80415