fix blank ai_canonname from getaddrinfo for non-CNAMEs
dynamically allocate storage for gethostby* buffers

this change shaves ~1k off libc.so bss size, and also avoids hard
errors in the case where the static buffer was not large enough to
hold the result.

this whole framework is really ugly and might should be replaced or at
least heavily overhauled when some changes/factorizations are made to
getaddrinfo internals in the future.
fix regression that made shared libs crash on arm
streamline old-kernel fallback path of pipe2 to use syscalls directly

also, don't waste code/time on F_GETFL since pipes always have blank
flags initially (at least on old kernels, which are all this fallback
code matters for).
overhaul posix_spawn to use CLONE_VM instead of vfork

the proposed change was described in detail in detail previously on
the mailing list. in short, vfork is unsafe because:

1. the compiler could make optimizations that cause the child to
clobber the parent's local vars.

2. strace is buggy and allows the vforking parent to run before the
child execs when run under strace.

the new design uses a close-on-exec pipe instead of vfork semantics to
synchronize the parent and child so that the parent does not return
before the child has finished using its arguments (and now, also its
stack). this also allows reporting exec failures to the caller instead
of giving the caller a child that mysteriously exits with status 127
on exec error.

basic testing has been performed on both the success and failure code
paths. further testing should be done.
fix unsigned comparison bug in posix_spawn

read should never return anything but 0 or sizeof ec here, but if it
does, we want to treat any other return as "success". then the caller
will get back the pid and is responsible for waiting on it when it
immediately exits.
base system() on posix_spawn

this avoids duplicating the fragile logic for executing an external
program without fork.
Makefile: make it possible to build arch specific C files
arm: add __aeabi_atexit()

arm eabi requires this symbol for static C++ dtors.
usually it is provided by libstdc++, but when a C++ program
doesn't use the std lib (free-standing), the libc has to provide
it.
this was encountered while building transmission, which
depends on such a C++ library (libutp).

this function is nearly identical to __cxa_atexit, but it has the
order of argumens swapped for "performance reasons".
see page 25 of

 http://infocenter.arm.com/help/topic/com.arm.doc.ihi0043d/IHI0043D_rtabi.pdf

there are other aeabi specific C++ support functions missing, but
it is not clear yet that GCC makes use of them so we omit them for
the moment.
improve error strings

this definitely has the potential to be a bikeshed topic, so some
justification is in order. most of the changes made fit into one of
the following categories:
1. alignment with text in posix, xsh 2.3
2. eliminating overly-specific text for shared error codes
3. making the message match more closely with the macro name
4. removing extraneous words

in particular, the EAGAIN/EWOULDBLOCK text is updated to match the
description of EAGAIN (which covers both uses) rather than saying the
operation would block, and ENOTSUP/EOPNOTSUPP is updated not to
mention sockets.

the distinction between ENFILE/EMFILE has also been clarified; ENFILE
is aligned with the posix text, and EMFILE, which lacks concise posix
text matching any historic message, is updated to emphasize that the
exhausted resource is not open files/open file descriptions, but
rather the integer 'address space' of file descriptors.

some messages may be further tweaked based on feedback.
fix typo in newly-added error message for EOWNERDEAD
add fgetgrent function

based on patch by Isaac Dunham, moved to its own file to avoid
increasing bss on static linked programs not using this nonstandard
function but using the standard getgrent function, and vice versa.
consistently use the internal name __environ for environ

patch by Jens Gustedt.
previously, the intended policy was to use __environ in code that must
conform to the ISO C namespace requirements, and environ elsewhere.
this policy was not followed in practice anyway, making things
confusing. on top of that, Jens reported that certain combinations of
link-time optimization options were breaking with the inconsistent
references; this seems to be a compiler or linker bug, but having it
go away is a nice side effect of the changes made here.
remove unused #undef environ now that libc.h no longer #defines it
Merge branch 'master' of git://git.musl-libc.org/musl into string
Fixes for strverscmp, take 2.

This uses size_t instead of int where appropriate, which drags in sys/types.h
Additionally, change from the more complex while loop
to a simpler one which exits earlier for equal strings.

More changes to follow.
More fixes for strverscmp.

-Change while (l++[0]) {lenl++;}
to while (l[lenl]) lenl++;
-As a result, we can drop two variables.
Aesthetic changes: *l instead of l[0].