strerrorname_np: Work around glibc bug on HPPA systems. * m4/strerrorname_np.m4 (gl_FUNC_STRERRORNAME_NP): Test also strerrorname_np (ENOSYM). * lib/strerrorname_np.c (strerrorname_np): Update comments. * tests/test-strerrorname_np.c (main): Likewise. * doc/glibc-functions/strerrorname_np.texi: Mention that glibc 2.37 still needs a workaround.