You can access the newlib source in a few ways:
cvs -z 9 -d :pserver:anoncvs@sources.redhat.com:/cvs/src login
{enter "anoncvs" as the password}
cvs -z 9 -d :pserver:anoncvs@sources.redhat.com:/cvs/src co newlib
You can use the cvsweb interface.
Source snapshots are available as gzipped tar files via anonymous FTP from the newlib ftp directory. New snapshots are packaged and released from time to time. Documentation snapshots are also provided.