divide select module into two modules: Unix and Win32 ones

auto/os/win32

@@ -10,6 +10,7 @@ CORE_SRCS="$WIN32_SRCS $IOCP_SRCS"
 OS_CONFIG="$WIN32_CONFIG"
 CORE_LIBS="$CORE_LIBS advapi32.lib ws2_32.lib"
 NGX_ICONS="$NGX_WIN32_ICONS"
+SELECT_SRCS=$WIN32_SELECT_SRCS
 
 EVENT_MODULES="$EVENT_MODULES $IOCP_MODULE"
 EVENT_FOUND=YES

auto/sources

@@ -95,6 +95,7 @@ EVENT_SRCS="src/event/ngx_event.c \
 
 SELECT_MODULE=ngx_select_module
 SELECT_SRCS=src/event/modules/ngx_select_module.c
+WIN32_SELECT_SRCS=src/event/modules/ngx_win32_select_module.c
 
 POLL_MODULE=ngx_poll_module
 POLL_SRCS=src/event/modules/ngx_poll_module.c