New module 'roundf-ieee'.

New module 'roundf-ieee'.

* modules/roundf-ieee: New file.
* m4/roundf.m4 (gl_FUNC_ROUNDF): If gl_FUNC_ROUNDF_IEEE is also used,
test whether roundf works according to ISO C 99 with IEC 60559.
* m4/roundf-ieee.m4: New file.
* modules/roundf-ieee-tests: New file.
* tests/test-roundf-ieee.c: New file, based on tests/test-roundf1.c.
* tests/test-roundf1.c (main): Remove signbit tests.
* modules/roundf-tests (Depends-on): Remove 'signbit'.
* doc/posix-functions/roundf.texi: Mention the new module.