[testsuite] don't use IBM 128-bit long double for IEEE tests

[Janis Johnson]

On Wed, 2008-08-27 at 19:51 +0000, Joseph S. Myers wrote:
> Which specific assertions do you find are unportable to IBM long double as 
> opposed to indicating compiler bugs?  Your analysis in PR 36332 says the 
> built-in functions are misclassifying __LDBL_MAX__, which would clearly be 
> a compiler bug, not a testcase bug.

Mea culpa.  I got sloppy and didn't look into it far enough this time,
and obvious forgot I had looked into this failure once before.

Janis