ceil: Implement result sign according to IEEE 754.

ceil: Implement result sign according to IEEE 754.

* lib/ceil.c (MIN, MINUS_ZERO): New macros.
(FUNC): Return -0.0 for -1 < x < 0.
* tests/test-ceil2.c: Include minus-zero.h.
(MINUS_ZERO): New macro.
(ceil_reference): Keep in sync with lib/ceil.c.
* tests/test-ceilf2.c: Include minus-zero.h.
(MINUS_ZERO): New macro.
(ceilf_reference): Keep in sync with lib/ceil.c.
* tests/test-ceilf-ieee.c (main): Test also values between -1 and 1.
* tests/test-ceil-ieee.c (main): Likewise.
* tests/test-ceill-ieee.c (main): Likewise.