The sched_setaffinity() function was introduced in DragonFly BSD 4.7,
so it is no longer Linux-specific.

Prodded by Sepherosa Ziehau.

This change allows setting the destination IPv6 address of a UDP datagram
received on a wildcard socket.

IPv6 now compiled-in automatically if support is found.  If there is a need
to disable it for some reason, --with-cc-opt="-DNGX_HAVE_INET6=0" can be used
for this.

This flag appeared in Linux 4.5 and is useful for avoiding thundering herd
problem.

The current Linux kernel implementation walks the list of exclusive waiters,
and queues an event to each epfd, until it finds the first waiter that has
threads blocked on it via epoll_wait().

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

The auto/module script is extended to understand ngx_module_link=DYNAMIC.
When set, it links the module as a shared object rather than statically
into nginx binary.  The module can later be loaded using the "load_module"
directive.

New auto/module parameter ngx_module_order allows to define module loading
order in complex cases.  By default the order is set based on ngx_module_type.

3rd party modules can be compiled dynamically using the --add-dynamic-module
configure option, which will preset ngx_module_link to "DYNAMIC" before
calling the module config script.

Win32 support is rudimentary, and only works when using MinGW gcc (which
is able to handle exports/imports automatically).

In collaboration with Ruslan Ermilov.

With this change it's no longer needed to pass -D_GNU_SOURCE manually,
and -D_FILE_OFFSET_BITS=64 is set to use 64-bit off_t.

Note that nginx currently fails to work properly with master process
enabled on GNU Hurd, as fcntl(F_SETOWN) returns EOPNOTSUPP for sockets
as of GNU Hurd 0.6.  Additionally, our strerror() preloading doesn't
work well with GNU Hurd, as it uses large numbers for most errors.