Unlike with GCC or MSVC, Clang linker doesn't auto-append ".exe" to the name
of the output binary when building on win32.

Dependencies of dynamic modules are added to NGX_ADDON_DEPS (and
it is now used for dynamic modules) to be in line with what happens
in case of static compilation.

To avoid duplication, MAIL_DEPS and STREAM_DEPS are no longer passed
to auto/module when these modules are compiled as dynamic ones.  Mail
and stream dependencies are handled explicitly via corresponding
variables.

Previously flags passed by --with-ld-opt were not used when building perl
module, which meant hardening flags provided by package build systems were not
applied.

Just using "cp" is incorrect, as it will overwrite old files
possibly used by OS, leading to unexpected effects.  Changed
to "mv + cp", much like used for the main binary.

Removed extraneous braces around shell variables.

The "build" target introduced to do all build-related tasks, and
it is now used in Makefile and in objs/Makefile as a dependency for
the "install" target.

In particular, this resolves problems as observed with dynamic modules
by people trying to do "make install" without calling "make" first.

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.

This script simplifies configuration of additional modules,
including 3rd party ones.  The script is extensible, and
will be used to introduce dynamic linking of modules in upcoming
changes.

3rd party module config scripts are called with ngx_module_link
preset to "ADDON" - this allows config scripts to call auto/module
without ngx_module_link explicitly defined, as well as testing if
new interface is in place if compatibility with older nginx versions
is desired.

In collaboration with Ruslan Ermilov.