move alignment check from aligned_alloc to posix_memalign

C11 has no requirement that the alignment be a multiple of
sizeof(void*), and in fact seems to require any "valid alignment
supported by the implementation" to work. since the alignment of char
is 1 and thus a valid alignment, an alignment argument of 1 should be
accepted.
move core memalign code from aligned_alloc to __memalign

there are two motivations for this change. one is to avoid
gratuitously depending on a C11 symbol for implementing a POSIX
function. the other pertains to the documented semantics. C11 does not
define any behavior for aligned_alloc when the length argument is not
a multiple of the alignment argument. posix_memalign on the other hand
places no requirements on the length argument. using __memalign as the
implementation of both, rather than trying to implement one in terms
of the other when their documented contracts differ, eliminates this
confusion.
add NFDBITS in sys/select.h with appropriate feature tests

the main use for this macro seems to be knowing the correct allocation
granularity for dynamic-sized fd_set objects. such usage is
non-conforming and results in undefined behavior, but it is widespread
in applications.
fix missing SOCK_CLOEXEC in various functions that use sockets internally
fix fd leak on races and cancellation in ctermid
fix bogus lazy allocation in ctermid and missing malloc failure check

also clean up, optimize, and simplify the code, removing branches by
simply pre-setting the result string to an empty string, which will be
preserved if other operations fail.
fix off-by-one array bound in strsignal
add realtime signals to strsignal

the name format RTnn/RTnnn was chosen to minimized bloat while
uniquely identifying the signal.
fix a couple misleading/wrong signal descriptions in strsignal

there are still several more that are misleading, but SIGFPE (integer
division error misdescribed as floating point) and and SIGCHLD
(possibly non-exit status change events described as exiting) were the
worst offenders.
fix invalid library phdr pointers passed to callback from dl_iterate_phdr

map_library was saving pointers to an automatic-storage buffer rather
than pointers into the mapping. this should be a fairly simple fix,
but the patch here is slightly complicated by two issues:

1. supporting gratuitously obfuscated ELF files where the program
headers are not right at the beginning of the file.

2. cleaning up the map_library function so that data isn't clobbered
by the time we need it.
add some ARM EABI-specific exception handling infrastructure

patch by Timo Teräs
add PIE support for ARM
fix omission of dtv setup in static linked programs on TLS variant I archs

apparently this was never noticed before because the linker normally
optimizes dynamic TLS models to non-dynamic ones when static linking,
thus eliminating the calls to __tls_get_addr which crash when the dtv
is missing. however, some libsupc++ code on ARM was calling
__tls_get_addr when static linked and crashing. the reason is unclear
to me, but with this issue fixed it should work now anyway.
the big time handling overhaul

this commit has two major user-visible parts: zoneinfo-format time
zones are now supported, and overflow handling is intended to be
complete in the sense that all functions return a correct result if
and only if the result fits in the destination type, and otherwise
return an error. also, some noticable bugs in the way DST detection
and normalization worked have been fixed, and performance may be
better than before, but it has not been tested.
fix fd leak in file mapping code used in new zoneinfo support
fix error code on time conversion overflows

POSIX mandates EOVERFLOW for this condition.
fix missing argument in variadic syscall macros

for 0-argument syscalls (1 argument to the macro, the syscall number),
the __SYSCALL_NARGS_X macro's ... argument was not satisfied. newer
compilers seem to care about this.
make posix_spawn (and functions that use it) use CLONE_VFORK flag

this is both a minor scheduling optimization and a workaround for a
difficult-to-fix bug in qemu app-level emulation.

from the scheduling standpoint, it makes no sense to schedule the
parent thread again until the child has exec'd or exited, since the
parent will immediately block again waiting for it.

on the qemu side, as regular application code running on an underlying
libc, qemu cannot make arbitrary clone syscalls itself without
confusing the underlying implementation. instead, it breaks them down
into either fork-like or pthread_create-like cases. it was treating
the code in posix_spawn as pthread_create-like, due to CLONE_VM, which
caused horribly wrong behavior: CLONE_FILES broke the synchronization
mechanism, CLONE_SIGHAND broke the parent's signals, and CLONE_THREAD
caused the child's exec to end the parent -- if it hadn't already
crashed. however, qemu special-cases CLONE_VFORK and emulates that
with fork, even when CLONE_VM is also specified. this also gives
incorrect semantics for code that really needs the memory sharing, but
posix_spawn does not make use of the vm sharing except to avoid
momentary double commit charge.

programs using posix_spawn (including via popen) should now work
correctly under qemu app-level emulation.
make spacing in x86_64 alltypes.h.sh more uniform with other archs

patch by Luka Perkov, who noted that all other archs have a newline.
fix FILENAME_MAX to match PATH_MAX

POSIX is not clear on whether it includes the termination, but ISO C
requires that it does. the whole concept of this macro is rather
useless, but it's better to be correct anyway.