hppa: Align __clone stack argument to 8 bytes (Bug 25066)

The hppa architecture requires strict alignment for loads and stores.
As a result, the minimum stack alignment that will work is 8 bytes.
This patch adjusts __clone() to align the stack argument passed to it.
It also adjusts slightly some formatting.

This fixes the nptl/tst-tls1 test.

(cherry picked from commit e4c23a02)