fix ecvt/fcvt decimal point position output

these functions are obsolete and have no modern standard. the text in
SUSv2 is highly ambiguous, specifying that "negative means to the left
of the returned digits", which suggested to me that 0 would mean to
the right of the first digit. however, this does not agree with
historic practice, and the Linux man pages are more clear, specifying
that a negative value means "that the decimal point is to the left of
the start of the string" (in which case, 0 would mean the start of the
string, in accordance with historic practice).
make fcvt decimal point location for zero make more sense

the (obsolete) standard allows either 0 or 1 for the decimal point
location in this case, but since the number of zero digits returned in
the output string (in this implementation) is one more than the number
of digits the caller requested, it makes sense for the decimal point
to be logically "after" the first digit. in a sense, this change goes
with the previous commit which fixed the value of the decimal point
location for non-zero inputs.
add Big5 charset support to iconv

at this point, it is just the common base charset equivalent to
Windows CP 950, with no further extensions. HKSCS and possibly other
supersets will be added later. other aliases may need to be added too.
sys/personality.h: add missing macros
sys/personality.h: add missing C++ compat
work around libraries with versioned symbols in dynamic linker

this commit does not add versioning support; it merely fixes incorrect
lookups of symbols in libraries that contain versioned symbols.
previously, the version information was completely ignored, and
empirically this seems to have resulted in the oldest version being
chosen, but I am uncertain if that behavior was even reliable.

the new behavior being introduced is to completely ignore symbols
which are marked "hidden" (this seems to be the confusing nomenclature
for non-current-version) when versioning is present. this should solve
all problems related to libraries with symbol versioning as long as
all binaries involved are up-to-date (compatible with the
latest-version symbols), and it's the needed behavior for dlsym under
all circumstances.
block signals during fork

there are several reasons for this. some of them are related to race
conditions that arise since fork is required to be async-signal-safe:
if fork or pthread_create is called from a signal handler after the
fork syscall has returned but before the subsequent userspace code has
finished, inconsistent state could result. also, there seem to be
kernel and/or strace bugs related to arrival of signals during fork,
at least on some versions, and simply blocking signals eliminates the
possibility of such bugs.
block all signals, even implementation-internal ones, in faccessat child

the child process's stack may be insufficient size to support a signal
frame, and there is no reason these signal handlers should run in the
child anyway.
fix missing errno from exec failure in posix_spawn

failures prior to the exec attempt were reported correctly, but on
exec failure, the return value contained junk.
optimize posix_spawn to avoid spurious sigaction syscalls

the trick here is that sigaction can track for us which signals have
ever had a signal handler set for them, and only those signals need to
be considered for reset. this tracking mask may have false positives,
since it is impossible to remove bits from it without race conditions.
false negatives are not possible since the mask is updated with atomic
operations prior to making the sigaction syscall.

implementation-internal signals are set to SIG_IGN rather than SIG_DFL
so that a signal raised in the parent (e.g. calling pthread_cancel on
the thread executing pthread_spawn) does not have any chance make it
to the child, where it would cause spurious termination by signal.

this change reduces the minimum/typical number of syscalls in the
child from around 70 to 4 (including execve). this should greatly
improve the performance of posix_spawn and other interfaces which use
it (popen and system).

to facilitate these changes, sigismember is also changed to return 0
rather than -1 for invalid signals, and to return the actual status of
implementation-internal signals. POSIX allows but does not require an
error on invalid signal numbers, and in fact returning an error tends
to confuse applications which wrongly assume the return value of
sigismember is boolean.
change sigset_t functions to restrict to _NSIG

the idea here is to avoid advertising signals that don't exist and to
make these functions safe to call (e.g. from within other parts of the
implementation) on fake sigset_t objects which do not have the HURD
padding.
add cpu affinity interfaces

this first commit just includes the CPU_* and sched_* interfaces, not
the pthread_* interfaces, which may be added later. simple
sanity-check testing has been done for the basic interfaces, but most
of the macros have not yet been tested.
add pthread_setaffinity_np and pthread_getaffinity_np functions
fix definitions of WIFSTOPPED and WIFSIGNALED to support up to signal 127

mips has signal numbers up to 127 (formerly, up to 128, but the last
one never worked right and caused kernel panic when used), so 127 in
the "signal number" field of the wait status is insufficient for
determining that the process was stopped. in addition, a nonzero value
in the upper bits must be present, indicating the signal number which
caused the process to be stopped.

details on this issue can be seen in the email with message id
CAAG0J9-d4BfEhbQovFqUAJ3QoOuXScrpsY1y95PrEPxA5DWedQ@mail.gmail.com on
the linux-mips mailing list, archived at:
http://www.linux-mips.org/archives/linux-mips/2013-06/msg00552.html
and in the associated thread about fixing the mips kernel bug.

commit 4a96b948687166da26a6c327e6c6733ad2336c5c fixed the
corresponding issue in uClibc, but introduced a multiple-evaluation
issue for the WIFSTOPPED macro.

for the most part, none of these issues affected pure musl systems,
since musl has up until now (incorrectly) defined SIGRTMAX as 64 on
all archs, even mips. however, interpreting status of non-musl
programs on mips may have caused problems. with this change, the full
range of signal numbers can be made available on mips.
fix _NSIG and SIGRTMAX on mips

a mips signal mask contains 128 bits, enough for signals 1 through
128. however, the exit status obtained from the wait-family functions
only has room for values up to 127. reportedly signal 128 was causing
kernelspace bugs, so it was removed from the kernel recently; even
without that issue, however, it was impossible to support it correctly
in userspace.

at the same time, the bug was masked on musl by SIGRTMAX incorrectly
yielding 64 on mips, rather than the "correct" value of 128. now that
the _NSIG issue is fixed, SIGRTMAX can be fixed at the same time,
exposing the full range of signals for application use.

note that the (nonstandardized) libc _NSIG value is actually one
greater than the max signal number, and also one greater than the
kernel headers' idea of _NSIG. this is the reason for the discrepency
with the recent kernel changes. since reducing _NSIG by one brought it
down from 129 to 128, rather than from 128 to 127, _NSIG/8, used
widely in the musl sources, is unchanged.
allow subarch-specific asm, including asm specific to the default

the default subarch is the one whose full name is just the base arch
name, with no suffixes. normally, either the asm in the default
subarch is suitable for all subarch variants, or separate asm is
mandatory for each variant. however, in the case of asm which is
purely for optimization purposes, it's possible to have asm that only
works (or only performs well) on the default subarch, and not any othe
the other variants. thus, I have added a mechanism to give a name to
the default variant, for example "armel" for the default,
little-endian arm. further such default-subarch names can be added in
the future as needed.
add missing a_or_l to atomic.h for non-x86 archs

this is needed for recently committed sigaction code
add subarch asm support for PIC objects/shared libc

this rule was omitted in previous subarch asm commit
provide declarations for strtod_l and family

these aliases were originally intended to be for ABI compatibility
only, but their presence caused regressions in broken gnulib-based
software whose configure scripts detect the existing of these
functions then use them without declarations, resulting in bogus
return values.
add missing MSG_EXCEPT in sys/msg.h