The semi-recent SYSCALL_CANCEL inclusion broke hppa due to the sysdep.h
headers not including the unix/sysdep.h headers. Rework the includes so
we match the other ports:
* hppa/sysdep.h:
- Do not include sys/syscall.h as the unix sysdep.h headers do it.
- Do not include config.h as libc-symbols.h does it, and it has no
#ifdef multiple-include protection, and it breaks when some files
do things like #undef __OPTIMIZE__.
* sysdeps/unix/sysv/linux/hppa/sysdep-cancel.h:
- Drop the generic/sysdep.h as the unix sysdep.h headers include it.
* sysdeps/unix/sysv/linux/hppa/sysdep.h:
- Change to the unix & core hppa sysdep header stacks.
- Undef a few defines that the core headers already set up for us.
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