update syscall defs to latest kernel ones

patch submitted by Kristian L. <email@thexception.net>
add process_vm_readv and process_vm_writev syscall wrappers

based on a patch submitted by Kristian L. <email@thexception.net>
release notes for 0.9.2
fix arm crti/crtn code

lr must be saved because init/fini-section code from the compiler
clobbers it. this was not a problem when i tested without gcc's
crtbegin/crtend files present, but with them, musl on arm fails to
work (infinite loop in _init).
replace old and ugly crypt implementation

the new version is largely the work of Solar Designer, with minor
changes for integration with musl. compared to the old code, text size
is reduced by about 7k, stack space usage by about 70k, and
performance is greatly improved by avoiding expensive calculation of
constant tables on each run.

this version also adds support for extended des-based password hashes,
which allow for unlimited key (password) length and configurable
iteration counts.

i've also published the interface for crypt_r in a new crypt.h header.
especially since this is not a standard interface, i did not feel
compelled to match the glibc abi for the crypt_data structure. the
glibc structure is way too big to allocate on the stack; in fact it's
so big that the first usage may cause the main thread to exceed its
pre-committed stack size of 128k and thus could cause the program to
crash even on systems with overcommit disabled. the only legitimate
use of crypt_data for crypt_r is to store the hash string to return,
so i've reserved 256 bytes, which should be more than sufficient
(longest known password hashes are ~60 characters, and beyond that is
possibly even exceeding some implementations' passwd file field size
limit).
fix invalid implicit pointer conversion in ld64 modfl
fix missing prototype and simplify sincosl on ld64 archs
fix missing function declarations for __stdio_exit
fix sigsetjmp on arm (needs asm)

no idea why gcc refuses to compile the C code to use a tail call, but
it's best to use asm anyway so we don't have to rely on the quality of
the compiler's optimizations for correct code.
jmp_buf overhaul fixing several issues

on arm, the location of the saved-signal-mask flag and mask were off
by one between sigsetjmp and siglongjmp, causing incorrect behavior
restoring the signal mask. this is because the siglongjmp code assumed
an extra slot was in the non-sig jmp_buf for the flag, but arm did not
have this. now, the extra slot is removed for all archs since it was
useless.

also, arm eabi requires jmp_buf to have 8-byte alignment. we achieve
that using long long as the type rather than with non-portable gcc
attribute tags.
configure: only use -ffloat-store on i386

this option is expensive and only used on old gcc's that lack
-fexcess-precision=standed, but it's not needed on non-i386 archs
where floating point does not have excess precision anyway.

if musl ever supports m68k, i think it will need to be special-cased
too. i'm not aware of any other archs with excess precision.
add prototypes for getw/putw
make sure getw/putw agree with prototypes by defining _GNU_SOURCE
putw is supposed to return 0 (not the value written) on success

this is not a standard but it's the traditional behavior and it's more
useful because the caller can reliably detect errors.
fix dlsym RTLD_NEXT support

previously this was being handled the same as a library-specific,
dependency-order lookup on the next library in the global chain, which
is likely to be utterly meaningless. instead the lookup needs to be in
the global namespace, but omitting the initial portion of the global
library chain up through the calling library.
remove little-endian assumption from arm atomic.h

this hidden endian dependency had left big endian arm badly broken.
make arm syscalls (still non-inline) more efficient

no need to pass zero for unused arguments; just omit them.
fix wrong value of FLT_EVAL_METHOD for x86_64
support -mfpmath=387 on x86_64

apparently somebody wants this for something... and it doesn't hurt.
fix lots of breakage on dlopen, mostly with explicit pathnames

most importantly, the name for such libs was being set from an
uninitialized buffer. also, shortname always had an initial '/'
character, making it useless for looking up already-loaded libraries
by name, and thus causing repeated searches through the library path.

major changes now:

- shortname is the base name for library lookups with no explicit
  pathname. it's initially clear for libraries loaded with an explicit
  pathname (and for the main program), but will be set if the same
  library (detected via inodes match) is later found by a search.

- exact name match is never used to identify libraries loaded with an
  explicit pathname. in this case, there's no explicit search, so we
  can just stat the file and check for inode match.