[PowerPC64] Correct IBM long double frexpl

[Joseph S. Myers]

On Tue, 25 Mar 2014, Alan Modra wrote:

> Besides fixing the bugzilla, this also fixes corner-cases where the high
> and low double differ greatly in magnitude, and handles a denormal
> input without resorting to a fp rescale.

Cases where the high and low double differ greatly in magnitude are bug 
16619 (such test inputs can't be represented in libm-test.inc, but you 
should see improvements in test results for clog10l; it was large errors 
from clog10l that drew my attention to problems with such cases).

-- 
Joseph S. Myers
joseph@codesourcery.com