hppa: Fix feupdateenv and fesetexceptflag (Bug 18111).

The function feupdateenv has been fixed to correctly handle FE_DFL_ENV
and FE_NOMASK_ENV.

The fesetexceptflag function has been fixed to correctly handle setting
the new flags instead of just OR-ing the existing flags.

This fixes the test-fenv-return and test-fenvinline failures on hppa.