New module 'truncf-ieee'.

New module 'truncf-ieee'.

* modules/truncf-ieee: New file.
* m4/truncf.m4 (gl_FUNC_TRUNCF): If gl_FUNC_TRUNCF_IEEE is also used,
test whether truncf works according to ISO C 99 with IEC 60559.
* m4/truncf-ieee.m4: New file.
* lib/math.in.h (truncf): Replace if REPLACE_TRUNCF is set.
* m4/math_h.m4 (gl_MATH_H_DEFAULTS): Initialize REPLACE_TRUNCF.
* modules/math (Makefile.am): Substitute REPLACE_TRUNCF.
* modules/truncf-ieee-tests: New file.
* tests/test-truncf-ieee.c: New file, based on tests/test-truncf1.c.
* tests/test-truncf1.c (main): Remove signbit tests.
* modules/truncf-tests (Depends-on): Remove 'signbit'.
* doc/posix-functions/truncf.texi: Mention the new module.