libstdc++: Update copyright dates on new files

libstdc++: Update copyright dates on new files

The patch adding these files was approved in 2020 but it wasn't
committed until 2021, so the copyright years were not updated along with
the years in all the existing files.

libstdc++-v3/ChangeLog:

	* include/std/barrier: Update copyright years. Fix whitespace.
	* include/std/version: Fix whitespace.
	* testsuite/30_threads/barrier/1.cc: Update copyright years.
	* testsuite/30_threads/barrier/2.cc: Likewise.
	* testsuite/30_threads/barrier/arrive.cc: Likewise.
	* testsuite/30_threads/barrier/arrive_and_drop.cc: Likewise.
	* testsuite/30_threads/barrier/arrive_and_wait.cc: Likewise.
	* testsuite/30_threads/barrier/completion.cc: Likewise.