Various pthread types on hppa-linux require an alignment of 16 bytes for ABI reasons.  This is larger
than the current implementations of max_align_t and max_align_t_align.  As a result, the patch to
implement C++17 over-aligned new  causes warnings on hppa.  The thread here discusses the problem:
https://gcc.gnu.org/ml/gcc-patches/2016-09/msg01593.html

The attached patch implements a new hook to allow overriding the default implementation of max_align_t_align
in the PA backend.  It changes the max_align_t alignment to 16 bytes on 32-bit hppa-linux.  I added an additional
comment to BIGGEST_ALIGNMENT in pa.h to document the alignment choices for long double on hpux.  I also
defined MALLOC_ABI_ALIGNMENT so that it reflects the behaviour of the glibc and hpux malloc implementations.

Tested on hppa2.0w-hp-hpux11.11, hppa64-hp-hpux11.11 and hppa-unknown-linux-gnu with no observed
regressions.

Okay for trunk?

Dave
--
John David Anglin	dave.anglin@bell.net