ceil, floor: avoid spurious failure with icc

ceil, floor: avoid spurious failure with icc

* tests/test-ceilf2.c (ceilf_reference): Avoid icc's use of DAZ
[denormals-as-zero] when optimizing without -mieee-fp option.
* tests/test-floorf2.c (floorf_reference): Likewise.
* tests/test-ceilf1.c (dummy): New function.
(main): Use it to outsmart icc's optimization.
* tests/test-floorf1.c (dummy, main): Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>