even with this change, PIE will not work yet due to deficiencies in
the crt1.o startup code.

even a single-threaded program can be cancellable, e.g. if it's called
pthread_cancel(pthread_self()). the correct predicate to check is not
whether multiple threads have been invoked, but whether pthread_self
has been invoked.

patch by sh4rm4

this allows the full range of 64-bit limit arguments even on 32-bit
systems. fallback to the old syscalls on old kernels that don't
support prlimit.

this fixes an issue using gold instead of gnu ld for linking. it also
should eliminate the need of the startup code to even load/pass the
got address to the dynamic linker.

based on patch submitted by sh4rm4 with minor cosmetic changes.

further cleanup will follow.

note that regardless of the name used, basename is always conformant.
it never takes on the bogus gnu behavior, unlike glibc where basename
is nonconformant when declared manually without including libgen.h.

this only affects non-ascii symbol names, which are probably not in
use anyway..

CHUNK_SIZE macro was defined incorrectly and shaving off at least one
significant bit in the size of mmapped chunks, resulting in the test
for oldlen==newlen always failing and incurring a syscall. fortunately
i don't think this issue caused any other observable behavior; the
definition worked correctly for all non-mmapped chunks where its
correctness matters more, since their lengths are always multiples of
the alignment.

patch by Pascal Cuoq (with minor tweaks to comments)

patch by Arvid Picciani (aep)

this is not required by the standard, but it's nicer than corrupting
the state and rather inexpensive.

note that none of these are implemented, and programs depending on
them may break... patch by sh4rm4

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

it's a keyword in c++ (wtf). i'm not sure this is the cleanest
solution; it might be better to avoid ever defining __NEED_wchar_t on
c++. but in any case, this works for now.

this may be useful to posix_spawn..?

musl's dynamic linker does not support unloading dsos, so there's
nothing for this function to do. adding the symbol in case anything
depends on its presence..

mildly tested; may have bugs. the locking should be updated not to use
spinlocks but that's outside the scope of this one module.

the fcntl syscall can return a negative value when the command is
F_GETOWN, and this is not an error code but an actual value. thus we
must special-case it and avoid calling __syscall_ret to set errno.
this fix is better than the glibc fix (using F_GETOWN_EX) which only
works on newer kernels and is more complex.

no idea why these 4 are permuted and the rest are standard/generic

...and still be valid in #if directives.

right now it's questionable whether this change is an improvement or
not, but if we later want to support priority inheritance mutexes, it
will be important to have the code paths unified like this to avoid
major code duplication.

this is valid for error-checking mutexes; otherwise it invokes UB and
would be justified in crashing.

this simplifies the code paths slightly, but perhaps what's nicer is
that it makes recursive mutexes fully reentrant, i.e. locking and
unlocking from a signal handler works even if the interrupted code was
in the middle of locking or unlocking.

a reader unlocking the lock need only wake one waiter (necessarily a
writer, but a writer unlocking the lock must wake all waiters
(necessarily readers). if it only wakes one, the remainder can remain
blocked indefinitely, or at least until the first reader unlocks (in
which case the whole lock becomes serialized and behaves as a mutex
rather than a read lock).

mildly tested, seems to work