fix regression in arm user.h that happened during big user.h changes

make sys/procfs.h mostly work on most archs

these structures are purely for use by trace/debug tools and tools
working with core files. the definition of fpregset_t, which was
previously here, has been removed because it was wrong; fpregset_t
should be the type used in mcontext_t, not the type used in
ptrace/core stuff.

begin sys/user.h and sys/reg.h fixes for ports

aside from microblaze, these should be roughly correct for all archs
now. some misc junk macros and typedefs are missing, which should
probably be added for max compatibility with trace/debug tools.

fix some details in ugly stuff that doesn't belong in libc

patches by sh4rm4, presumably needed to make gdb or some similar junk
happy...

initial commit of the arm port

this port assumes eabi calling conventions, eabi linux syscall
convention, and presence of the kernel helpers at 0xffff0f?0 needed
for threads support. otherwise it makes very few assumptions, and the
code should work even on armv4 without thumb support, as well as on
systems with thumb interworking. the bits headers declare this a
little endian system, but as far as i can tell the code should work
equally well on big endian.

some small details are probably broken; so far, testing has been
limited to qemu/aboriginal linux.