ceill-ieee: Make it work on OSF/1 5.1 with cc. * doc/posix-functions/ceill.texi: Mention the OSF/1 5.1 bug. * m4/ceill.m4 (gl_FUNC_CEILL): If gl_FUNC_CEILL_IEEE is also used, test whether ceill works according to ISO C 99 with IEC 60559. * m4/ceill-ieee.m4: New file. * modules/ceill-ieee (Files): Add it and m4/minus-zero.m4, m4/signbit.m4. (configure.ac): Invoke gl_FUNC_CEILL_IEEE.