remainderf-ieee: Work around test failure on OSF/1. * m4/remainderf-ieee.m4: New file. * m4/remainderf.m4 (gl_FUNC_REMAINDERF): If gl_FUNC_REMAINDERF_IEEE is present, test whether remainderf works with a zero second argument. Replace it if not. * lib/math.in.h (remainderf): Override if REPLACE_REMAINDERF is 1. * m4/math_h.m4 (gl_MATH_H_DEFAULTS): Initialize REPLACE_REMAINDERF. * modules/math (Makefile.am): Substitute REPLACE_REMAINDERF. * modules/remainderf (configure.ac): Consider REPLACE_REMAINDERF. (Depends-on): Update conditions. * modules/remainderf-ieee (Files): Add m4/remainderf-ieee.m4. (Depends-on): Add remainder-ieee. (configure.ac): Invoke gl_FUNC_REMAINDERF_IEEE. * doc/posix-functions/remainderf.texi: Mention the remainderf-ieee module.