Fix backtrace for hppa (bug 22719).

The only architecture in glibc that uses the generic debug/backtrace.c
is hppa.  The debug/tst-backtrace* tests fail for hppa, so in fact the
generic debug/backtrace.c is not functional anywhere.  Instead, the
x86_64 version is a reasonably generic version that uses
_Unwind_Backtrace from libgcc to backtrace using unwind info, and is
used by several architectures.  This patch adds hppa to the
architectures using it (leaving open the possibility of a subsequent
cleanup for 2.28 of moving the x86_64 version to debug/backtrace.c,
and removing all the frame.h files that are now unused).

Reported by Adhemerval in
<https://sourceware.org/ml/libc-alpha/2018-01/msg00564.html> that this
does fix the backtrace test failures for hppa.

	[BZ #22719]
	* sysdeps/hppa/backtrace.c: New file.