Fix ChangeLog indentation.
PowerPC: Move powerpc code out of nptl/ subdirectory
PowerPC: Fix nearbyintl failure for few inputs

This patch fixes few failures in nearbyintl() where the fraction part is
close to 0.5.i  The new tests added report few extra failures in
nearbyint_downward and nearbyint_towardzero which is a known issue.

Fixes #17031.