PR libstdc++/83626 handle ENOENT due to filesystem race

PR libstdc++/83626 handle ENOENT due to filesystem race

	PR libstdc++/83626
	* src/filesystem/ops.cc (remove(const path&, error_code&)): Do not
	report an error for ENOENT.
	(remove_all(const path&)): Fix type of result variable.
	(remove_all(const path&, error_code&)): Use non-throwing increment
	for directory iterator. Call POSIX remove directly to avoid redundant
	calls to symlink_status. Do not report errors for ENOENT.
	* src/filesystem/std-ops.cc: Likewise.
	* testsuite/27_io/filesystem/operations/remove_all.cc: Test throwing
	overload.
	* testsuite/experimental/filesystem/operations/remove_all.cc:
	Likewise.

From-SVN: r256283