These constants are not specified by POSIX, but they are in the reserved
namespace, glibc and bsd systems seem to provide them as well.
(Note that POSIX specifies -NZERO and NZERO-1 to be the limits, but
PRIO_MAX equals NZERO)

low latency busy poll sockets are new in linux v3.11

PTRACE_GETSIGMASK and PTRACE_SETSIGMASK were added in linux v3.11
and used by checkpoint/restore tools

this is ugly and useless, but it seems to be the least-ugly way to
provide it...

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.