alternatively, we could define it in sys/socket.h since SO* is
reserved there, and tcp.h includes sys/socket.h in extensions mode.

note that SOL_TCP is simply wrong and it's only here for compatibility
with broken applications. the correct argument to pass for setting TCP
socket options is IPPROTO_TCP, which of course has the same value as
SOL_TCP but works everywhere.

report/patch by Hiltjo Posthuma <hiltjo@codemadness.org>

this is a trivial no-op, because dlclose never deletes libraries. thus
we might as well have it in the header in case some application wants
it, since we're already providing it anyway.

based on patch by Pierre Carrier <pierre@gcarrier.fr> that just added
the flag constant, but with minimal additional code so that it
actually works as documented. this is a nonstandard option but some
major software (reportedly, Firefox) uses it and it was easy to add
anyway.

the historical mess of having different definitions for C and C++
comes from the historical C definition as (void *)0 and the fact that
(void *)0 can't be used in C++ because it does not convert to other
pointer types implicitly. however, using plain 0 in C++ exposed bugs
in C++ programs that call variadic functions with NULL as an argument
and (wrongly; this is UB) expect it to arrive as a null pointer. on
64-bit machines, the high bits end up containing junk. glibc dodges
the issue by using a GCC extension __null to define NULL; this is
observably non-conforming because a conforming application could
observe the definition of NULL via stringizing and see that it is
neither an integer constant expression with value zero nor such an
expression cast to void.

switching to 0L eliminates the issue and provides compatibility with
broken applications, since on all musl targets, long and pointers have
the same size, representation, and argument-passing convention. we
could maintain separate C and C++ definitions of NULL (i.e. just use
0L on C++ and use (void *)0 on C) but after careful analysis, it seems
extremely difficult for a C program to even determine whether NULL has
integer or pointer type, much less depend in subtle, unintentional
ways, on whether it does. C89 seems to have no way to make the
distinction. on C99, the fact that (int)(void *)0 is not an integer
constant expression, along with subtle VLA/sizeof semantics, can be
used to make the distinction, but many compilers are non-conforming
and give the wrong result to this test anyway. on C11, _Generic can
trivially make the distinction, but it seems unlikely that code
targetting C11 would be so backwards in caring which definition of
NULL an implementation uses.

as such, the simplest path of using the same definition for NULL in
both C and C++ was chosen. the #undef directive was also removed so
that the compiler can catch and give a warning or error on
redefinition if buggy programs have defined their own versions of
NULL prior to inclusion of standard headers.

struct dso was not defined in this case, and it's not needed in the
code that was using it anyway; void pointers work just as well.

some structs and functions had reference to the params
feature of tre that is not used by the code anymore

pos_start local variable is not used in tre_tnfa_run_backtrack

original FreeSec code accessed keybuf as uint32* and uint8* as well
(incorrectly), this got fixed with an union, but then it seems the
uint32* access is no longer needed so the code can be simplified

the internal sha2 hash sum functions had incorrect array size
in the prototype for the message digest argument, fixed by
using pointer so it is not misleading

added various MS_*, MNT_*, UMOUNT_* flags following the linux
headers, with one exception: MS_NOUSER is defined as (1U<<31)
instead of (1<<31) which invokes undefined behaviour

the S_* flags were removed following glibc

using the glibc names for the magic constants of the linux reboot syscall

mips and powerpc already had this termios flag defined

it was already defined for mips, but was missing from other archs

based on linux headers add the missing MCAST_* options
under _GNU_SOURCE as they are not in the reserved namespace
(this api was originally specified by RFC 3678)

missing protocol families based on current linux headers:
PF_RDS, PF_LLC, PF_CAN, PF_TIPC, PF_NFC

this is wasteful and useless from a standpoint of sane programs, but
it is required by the standard, and the current requirements were
upheld with the closure of Austin Group issue #639:
http://austingroupbugs.net/view.php?id=639

common part of erf and erfc was put in a separate function which
saved some space and the new code is using unsigned arithmetics

erfcf had a bug: for some inputs in [7.95,8] the result had
more than 60ulp error: in expf(-z*z - 0.5625f) the argument
must be exact but not enough lowbits of z were zeroed,
-SET_FLOAT_WORD(z, ix&0xfffff000);
+SET_FLOAT_WORD(z, ix&0xffffe000);
fixed the issue

the anonymous struct typedef with array notation breaks with
GCC in C++ mode:

error: non-local function 'static<anonymous struct>
(& boost::signal_handler::jump_buffer())[1]' uses anonymous type

this is a known GCC issue, as search results for that error msg
suggest.

since this is hard to work around in the calling C++ code, a
fix in musl is preferable.

some programs (procps, babl) expect it, and it doesn't seem to
cause any harm to just add it.
it's small and straightforward.

since math.h also defines MAXFLOAT, we undef it in both places,
before defining it.

these flags are needed in order to be able to handle lwp id's
which the kernel returns after clone() calls for new threads
via ptrace(PTRACE_GETEVENTMSG).

fortunately, they're the same for all archs and in the reserved
namespace.

for _Noreturn functions, gcc generates code that trashes the
stack frame, and so it makes it impossible to inspect the causes
of an assert error in gdb.

abort() is not affected (i have not yet investigated why).

both jn and yn functions had integer overflow issues for large
and small n

to handle these issues nm1 (== |n|-1) is used instead of n and -n
in the code and some loops are changed to make sure the iteration
counter does not overflow

(another solution could be to use larger integer type or even double
but that has more size and runtime cost, on x87 loading int64_t or
even uint32_t into an fpu register is more than two times slower than
loading int32_t, and using double for n slows down iteration logic)

yn(-1,0) now returns inf

posix2008 specifies that on overflow and at +-0 all y0,y1,yn functions
return -inf, this is not consistent with math when n<0 odd integer in yn
(eg. when x->0, yn(-1,x)->inf, but historically yn(-1,0) seems to be
special cased and returned -inf)

some threshold values in jnf and ynf were fixed that seems to be
incorrectly copy-pasted from the double version

a common code path in j1 and y1 was factored out so the resulting
object code is a bit smaller

unsigned int arithmetics is used for bit manipulation

j1(-inf) now returns 0 instead of -0

an incorrect threshold in the common code of j1f and y1f got fixed
(this caused spurious overflow and underflow exceptions)

the else branch in pone and pzero functions are fixed
(so code analyzers dont warn about uninitialized values)

a common code path in j0 and y0 was factored out so the resulting
object code is smaller

unsigned int arithmetics is used for bit manipulation

the logic of j0 got a bit simplified (x < 1 case was handled
separately with a bit higher precision than now, but there are large
errors in other domains anyway so that branch has been removed)

some threshold values were adjusted in j0f and y0f

reported/requested by Strake; simplified from the provided patch