this is equivalent to posix_fallocate except that it has an extra
mode/flags argument to control its behavior, and stores the error in
errno rather than returning an error code.

the syscall takes an extra flag argument which should be zero to meet
the POSIX requirements.

features.h contains the fallback logic for pre-C11 compilers

the old behavior of exposing nothing except plain ISO C can be
obtained by defining __STRICT_ANSI__ or using a compiler option (such
as -std=c99) that predefines it. the new default featureset is POSIX
with XSI plus _BSD_SOURCE. any explicit feature test macros will
inhibit the default.

installation docs have also been updated to reflect this change.

clang does not presently support the "v" constraint we want to use to
get the result from $3, and trying to use register...__asm__("$3") to
do the same invokes serious compiler bugs. so for now, i'm working
around the issue with an extra temp register and putting $3 in the
clobber list instead of using it as output. when the bugs in clang are
fixed, this issue should be revisited to generate smaller/faster code
like what gcc gets.

previously, it was pretty much random which one of these trees a given
function appeared in. they have now been organized into:

src/linux: non-POSIX linux syscalls (possibly shard with other nixen)
src/legacy: various obsolete/legacy functions, mostly wrappers
src/misc: still mostly uncategorized; some misc POSIX, some nonstd
src/crypt: crypt hash functions

further cleanup will be done later.

void* does not implicitly convert to function pointer types.

so far, this is the only actual use of loff_t i've found. some
software, including glib, assumes loff_t must exist if splice exists;
this is a reasonable assumption since the official prototype for
splice uses loff_t, as it always works with 64-bit offsets regardless
of the selected libc off_t size. i'm using #define for now rather than
a typedef to make it easy to define in other headers if necessary
(like the LFS64 ugliness), but it may be necessary to add it to
alltypes.h eventually if other functions end up needing it.

note that POSIX does not specify these functions as _Noreturn, because
POSIX is aligned with C99, not the new C11 standard. when POSIX is
eventually updated to C11, it will almost surely give these functions
the _Noreturn attribute. for now, the actual _Noreturn keyword is not
used anyway when compiling with a c99 compiler, which is what POSIX
requires; the GCC __attribute__ is used instead if it's available,
however.

in a few places, I've added infinite for loops at the end of _Noreturn
functions to silence compiler warnings. presumably
__buildin_unreachable could achieve the same thing, but it would only
work on newer GCCs and would not be portable. the loops should have
near-zero code size cost anyway.

like the previous _Noreturn commit, this one is based on patches
contributed by philomath.

to deal with the fact that the public headers may be used with pre-c99
compilers, __restrict is used in place of restrict, and defined
appropriately for any supported compiler. we also avoid the form
[restrict] since older versions of gcc rejected it due to a bug in the
original c99 standard, and instead use the form *restrict.

unlike the memmove commit, this one should be fine to leave in place.
wmemmove is not performance-critical, and even if it were, it's
already copying whole 32-bit words at a time instead of bytes.

this commit introduces a performance regression in many uses of
memmove, which will need to be addressed before the next release. i'm
making it as a temporary measure so that the restrict patch can be
committed without invoking undefined behavior when memmove calls
memcpy with overlapping regions.

while musl itself requires a c99 compiler, some applications insist on
being compiled with c89 compilers, and use of "inline" in the headers
was breaking them. much of this had been avoided already by just
skipping the inline keyword in pre-c99 compilers or modes, but this
new unified solution is cleaner and may/should result in better code
generation in the default gcc configuration.

this should not break anything since the type should never be used
except as the argument type for poll.

all of the limits could use review, but err on the side of avoiding
excessive rounds for now.

these limits could definitely use review, but for now, i feel
consistency and erring on the side of preventing servers from getting
bogged down by excessively-slow user-provided settings (think
.htpasswd) are the best policy. blowfish should be updated to match.

based on versions sent to the list by nsz, with some simplification
and debloating. i'd still like to get them a bit smaller, or ideally
merge them into a single file with most of the code being shared, but
that can be done later.

if needed for debugging, it will be output in the .debug_frame section
instead, where it is not part of the loaded program and where the
strip command is free to strip it.

based on patches submitted by boris brezillon. this commit also fixes
the issue whereby the main application and libc don't have the address
ranges of their mappings stored, which was theoretically a problem for
RTLD_NEXT support in dlsym; it didn't actually matter because libc
never calls dlsym, and it seemed to be doing the right thing (by
chance) for symbols in the main program as well.

based on Gregor's patch sent to the list. includes:
- stdalign.h
- removing gets in C11 mode
- adding aligned_alloc and adjusting other functions to use it
- adding 'x' flag to fopen for exclusive mode

wrong hash was being passed; just a copy/paste error. did not affect
lookups in the global namespace; this is probably why it was not
caught in testing.

previously, this usage could lead to a crash if the thread pointer was
still uninitialized, and otherwise would just cause the canary to be
zero (less secure).

based on the patches contributed by boris brezillon.