libstdc++: Handle EPERM for filesystem access errors on MacOS [PR 99537]

libstdc++: Handle EPERM for filesystem access errors on MacOS [PR 99537]

Contrary to what POSIX says, some directory operations on MacOS can fail
with EPERM instead of EACCES, so we need to handle both.

libstdc++-v3/ChangeLog:

	PR libstdc++/99537
	* src/c++17/fs_dir.cc (recursive_directory_iterator): Use new
	helper function to check for permission denied errors.
	* src/filesystem/dir.cc (recursive_directory_iterator):
	Likewise.
	* src/filesystem/dir-common.h (is_permission_denied_error): New
	helper function.