PR_SET_MM_MAP was introduced as a subcommand for PR_SET_MM in
linux v3.18 commit f606b77f1a9e362451aca8f81d8f36a3a112139e

the associated struct type is replicated in sys/prctl.h using
libc types.

example usage:

 struct prctl_mm_map *p;
 ...
 prctl(PR_SET_MM, PR_SET_MM_MAP, p, sizeof *p);

the kernel side supported struct size may be queried with
the PR_SET_MM_MAP_SIZE subcommand.

there is no blksize64_t (blksize_t is always long) but there are
fsblkcnt64_t and fsfilcnt64_t types in sys/stat.h and sys/types.h.
and glob.h missed glob64_t.

they can be used to set or query if transparent huge pages are disabled.
introduced in linux 3.15 commit a0715cc22601e8830ace98366c0c2bd8da52af52

these are not pure syscall wrappers because they have to work around
kernel API bugs on 64-bit archs. the workarounds could probably be
made somewhat more efficient, but at the cost of more complexity. this
may be revisited later.

int8_t, u_int8_t, etc types are moved under _BSD_SOURCE

this was introduced to query BPF extension support with getsockopt
in linux 3.14, commit ea02f9411d9faa3553ed09ce0ec9f00ceae9885e

The mips arch is special in that it uses different RLIMIT_
numbers than other archs, so allow bits/resource.h to override
the default RLIMIT_ numbers (empty on all archs except mips).
Reported by orc.

in a sense this implementation is incomplete since it doesn't provide
the HWCAP_* macros for use with AT_HWCAP, which is perhaps the most
important intended usage case for getauxval. they will be added at a
later time.

the definition was found to be incorrect at least for powerpc, and
fixing this cleanly requires making the definition arch-specific. this
will allow cleaning up the definition for other archs to make it more
specific, and reversing some of the ugliness (time_t hacks) introduced
with the x32 port.

this first commit simply copies the existing definition to each arch
without any changes. this is intentional, to make it easier to review
changes made on a per-arch basis.

this was problematic because several archs don't define __WORDSIZE. we
could add it, but I would rather phase this macro out in the long
term. in our version of the headers, UINTPTR_MAX is available here, so
just use it instead.