New module 'trunc-ieee'.

New module 'trunc-ieee'.

* modules/trunc-ieee: New file.
* m4/trunc.m4 (gl_FUNC_TRUNC): If gl_FUNC_TRUNC_IEEE is also used, test
whether trunc works according to ISO C 99 with IEC 60559.
* m4/trunc-ieee.m4: New file.
* lib/math.in.h (trunc): Replace if REPLACE_TRUNC is set.
* m4/math_h.m4 (gl_MATH_H_DEFAULTS): Initialize REPLACE_TRUNC.
* modules/math (Makefile.am): Substitute REPLACE_TRUNC.
* modules/trunc-ieee-tests: New file.
* tests/test-trunc-ieee.c: New file, based on tests/test-truncf-ieee.c.
* tests/test-trunc1.c (main): Remove signbit tests.
* modules/trunc-tests (Depends-on): Remove 'signbit'.
* doc/posix-functions/trunc.texi: Mention the new module.