Dynamic modules.

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.

auto/os/darwin

@@ -14,6 +14,9 @@ CORE_SRCS="$UNIX_SRCS $DARWIN_SRCS"
 ngx_spacer='
 '
 
+MAIN_LINK=
+MODULE_LINK="-shared -Wl,-undefined,dynamic_lookup"
+
 # kqueue
 
 echo " + kqueue found"

auto/os/win32

@@ -12,10 +12,15 @@ OS_CONFIG="$WIN32_CONFIG"
 NGX_ICONS="$NGX_WIN32_ICONS"
 SELECT_SRCS=$WIN32_SELECT_SRCS
 
+ngx_pic_opt=
+
 case "$NGX_CC_NAME" in
 
     gcc)
         CORE_LIBS="$CORE_LIBS -ladvapi32 -lws2_32"
+        MAIN_LINK="$MAIN_LINK -Wl,--export-all-symbols"
+        MAIN_LINK="$MAIN_LINK -Wl,--out-implib=$NGX_OBJS/libnginx.a"
+        MODULE_LINK="-shared -L $NGX_OBJS -lnginx"
     ;;
 
     *)