in fcntl, avoid passing pointer arguments to syscalls as longs

really, fcntl should be changed to use the correct type corresponding
to cmd when calling va_arg, and to carry the correct type through
until making the syscall. however, this greatly increases binary size
and does not seem to offer any benefits except formal correctness, so
I'm holding off on that change for now.

the minimal changes made in this patch are in preparation for addition
of the x32 port, where the syscall macros need to know whether their
arguments are pointers or integers in order to properly pass them to
the 64-bit kernel.
fix type of semctl variadic argument

per POSIX, the variadic argument has type union semun, which may
contain a pointer or int; the type read depends on the command being
issued. this allows the userspace part of the implementation to be
type-correct without requiring special-casing for different commands.
the kernel always expects to receive the argument interpreted as
unsigned long (or equivalently, a pointer), and does its own handling
of extracting the int portion from the representation, as needed.

this change fixes two possible issues: most immediately, reading the
argument as a (signed) long and passing it to the syscall would
perform incorrect sign-extension of pointers on the upcoming x32
target. the other possible issue is that some archs may use different
(user-space) argument-passing convention for unions, preventing va_arg
from correctly obtaining the argument when the type long (or even
unsigned long or void *) is passed to it.
math: add drem and dremf weak aliases to i386 remainder asm

weak_alias was only in the c code, so drem was missing on platforms
where remainder is implemented in asm.
add __isoc99_vfscanf weak alias to vfscanf

this glibc abi compatibility function was missed when the scanf
aliases were added.
fix inadvertent use of struct in place of union for semun
fix remaining known namespace violations for netinet/in.h

the imr_, imsf_, ip6_, ip6m_, ipi_, ipi6_, SCM_, and SOL_ prefixes are
not in the reserved namespace for this header. thus the constants and
structures using them need to be protected under appropriate feature
test macros.

this also affects some headers which are permitted to include
netinet/in.h, particularly netdb.h and arpa/inet.h.

the SOL_ macros are moved to sys/socket.h where they are in the
reserved namespace (SO*). they are still accessible via netinet/in.h
since it includes sys/socket.h implicitly (which is permitted).

the SCM_SRCRT macro is simply removed, since the definition used for
it, IPV6_RXSRCRT is not defined anywhere. it could be re-added, this
time in sys/socket.h, if the appropriate value can be determined;
however, given that the erroneous definition was not caught, it is
unlikely that any software actually attempts to use SCM_SRCRT.
fix namespace violations in termios.h, at least mostly

the fix should be complete on archs that use the generic definitions
(i386, arm, x86_64, microblaze), but mips and powerpc have not been
checked thoroughly and may need more fixes.
add IUTF8 to termios.h on archs that were missing it
fix namespace violations in utmpx.h
fix namespace violation in sys/shm.h

in fixing this, I've changed the logic from ugly #if/#else blocks
inside the struct shm_info definition to a fixed struct definition and
optional macros to rename the elements. this will be helpful if we
need to move shm_info to a bits header in the future, as it will keep
the feature test logic out of bits.