New module 'round-ieee'.

New module 'round-ieee'.

* modules/round-ieee: New file.
* m4/round.m4 (gl_FUNC_ROUND): If gl_FUNC_ROUND_IEEE is also used, test
whether round works according to ISO C 99 with IEC 60559.
* m4/round-ieee.m4: New file.
* modules/round-ieee-tests: New file.
* tests/test-round-ieee.c: New file, based on tests/test-roundf-ieee.c.
* tests/test-round1.c (main): Remove signbit tests.
* modules/round-tests (Depends-on): Remove 'signbit'.
* doc/posix-functions/round.texi: Mention the new module.