previously, a common __posix_spawnx backend was used that accepted an
additional argument for the execve variant to call in the child. this
moderately bloated up the posix_spawn function, shuffling arguments
between stack and/or registers to call a 7-argument function from a
6-argument one.

instead, tuck the exec function pointer in an unused part of the
(large) pthread_spawnattr_t structure, and have posix_spawnp duplicate
the attributes and fill in a pointer to __execvpe. the net code size
change is minimal, but the weight is shifted to the "heavier" function
which already pulls in more dependencies.

as a bonus, we get rid of an external symbol (__posix_spawnx) that had
no really good place for a declaration because it shouldn't have
existed to begin with.

these are not public interfaces and do not match the public function,
but delegate argument checking to it.

this is not a public interface, and does not even necessarily match
the syscall on all archs that have a syscall by that name.

on archs where it's implemented in C, no action on the source file is
needed; the hidden declaration in pthread_arch.h suffices.

these are not a public interface and are not intended to be callable
from anywhere but the public clone function or other places in libc.

locale_impl.h could have been used, but this function is completely
independent of anything else, and preserving that property seems nice.

this functions is glue for linking dependency logic.

it's already included in all places where these are needed, and aside
from __tls_get_addr, they're all implementation internals.

this is a helper function from strftime that's also used by wcsftime.

this function was added later for strftime use and the existence of
time_impl.h as the appropriate place for it seems to have been
overlooked.

unlike the other res/dn functions, this one is tied to struct
resolvconf which is not a public interface, so put it in the private
header for its subsystem.

obviously the type "should be" const, but it inherited non-const from
the standard nl_langinfo_l.

despite looking like undefined behavior, the affected code is correct
both before and after this patch. the pairs mtx_t and pthread_mutex_t,
and cnd_t and pthread_cond_t, are not mutually compatible within a
single translation unit (because they are distinct untagged aggregate
instances), but they are compatible with an object of either type from
another translation unit (6.2.7 ¶1), and therefore a given translation
unit can choose which one it wants to use.

in the interest of being able to move declarations out of source files
to headers that facilitate checking, use the pthread type names in
declaring the namespace-safe versions of the pthread functions and
cast the argument pointer types when calling them.

the source file for this function is completely standalone, but it
doesn't seem worth adding a header just for it, so declare it in
lookup.h for now.

without this, it's plausible that assembler or linker could complain
about an unsatisfiable relocation.

eliminate gratuitous glue function for reporting the version, which
was probably leftover from the old dynamic linker design which lacked
a clear barrier for when/how it could access global data. put the
declaration for the data object that replaces it in libc.h where it
can be type checked.

logically these belong to the intersection of the stdio and pthread
subsystems, and either place the declarations could go (stdio_impl.h
or pthread_impl.h) requires a forward declaration for one of the
argument types.

these exist for the sake of defining the corresponding weak public
aliases (for C11 and POSIX namespace conformance reasons). they are
not referenced by anything else in libc, so make them static.

get rid of a gratuitous translation unit and call frame between
asctime_r and the actual implementation of the function. this is the
way gmtime_r and localtime_r are already done.

syscall.h was chosen as the header to declare it, since its intended
usage is alongside syscalls as a fallback for operations the direct
syscall does not support.

policy is that all public functions which have a public declaration
should be defined in a context where that public declaration is
visible, to avoid preventable type mismatches.

an audit performed using GCC's -Wmissing-declarations turned up the
violations corrected here. in some cases the public header had not
been included; in others, a feature test macro needed to make the
declaration visible had been omitted.

in the case of gethostent and getnetent, the omission seems to have
been intentional, as a hack to admit a single stub definition for both
functions. this kind of hack is no longer acceptable; it's UB and
would not fly with LTO or advanced toolchains. the hack is undone to
make exposure of the declarations possible.

this cleans up what had become widespread direct inline use of "GNU C"
style attributes directly in the source, and lowers the barrier to
increased use of hidden visibility, which will be useful to recovering
some of the efficiency lost when the protected visibility hack was
dropped in commit dc2f368e, especially
on archs where the PLT ABI is costly.

__pthread_mutex_timedlock is used to implement c11 mutex functions,
and therefore cannot call pthread_mutex_trylock by name.

compiler cannot cache immutable fields of the mutex object across
external calls it can't see, much less across atomics.

avoid gratuitously setting up and tearing down the robust list pending
slot.

this fix was intended to be amended in before release, but somehow got
missed.

This lets fexecve work even when /proc isn't mounted.

commit 4f35eb75 introduced this bug.
it is not present in any released versions. inadvertent use of the &
operator on an array into which we're indexing produced arithmetic on
the wrong-type pointer, with undefined behavior.

this code in sigaction was the only place where sizeof was being
applied to the kernel sigaction's mask member to get the size argument
to pass to the kernel. everywhere else, _NSIG/8 is used for this
purpose.

Linux makes this surprisingly difficult, but it can be done. the trick
here is using the fact that we control the implementation of sigaction
to prevent changing the disposition of SIGABRT to anything but SIG_DFL
after abort has tried and failed to terminate the process simply by
calling raise(SIGABRT).