hppa: Drop 16-byte pthread lock alignment

Linux threads were removed about 12 years ago and the current
nptl implementation only requires 4-byte alignment for pthread
locks.

The 16-byte alignment causes various issues. For example in
building ignition-msgs, we have:

/usr/include/google/protobuf/map.h:124:37: error: static assertion failed
  124 |   static_assert(alignof(value_type) <= 8, "");
      |                 ~~~~~~~~~~~~~~~~~~~~^~~~

This is caused by the 16-byte pthread lock alignment.

Signed-off-by: John David Anglin <dave.anglin@bell.net>