How to make a C++ -module?

[Patrick Welche]

I'm trying to create a C++ loadable module. I thought it would be as easy
as:

======================= configure.ac ===================================
AC_INIT(hellow, 0.0.1)
AC_CONFIG_MACRO_DIR(m4)
AC_PROG_CXX
AM_INIT_AUTOMAKE([foreign])
LT_INIT
AC_CONFIG_FILES(Makefile)
AC_OUTPUT
======================= Makefile.am ====================================
lib_LTLIBRARIES = hellow.la

hellow_la_SOURCES = hellow.cpp
hellow_la_LDFLAGS = -module -avoid-version
======================= hellow.cpp =====================================
#include <iostream>

void myfunc(void)
{
        std::cout << "You called myfunc()!" << std::endl;
}
========================================================================

This fails with:

/bin/sh ./libtool  --tag=CXX   --mode=link g++  -g -O2 -module -avoid-version  
-o hellow.la -rpath /usr/local/lib hellow.lo  

*** Warning: linker path does not have real file for library -lgcc.
*** I have the capability to make that library automatically link in when
*** you link to this library.  But I can only do this if you have a
*** shared version of the library, which you do not appear to have
*** because I did check the linker path looking for a file starting
*** with libgcc and none of the candidates passed a file format test
*** using a regex pattern. Last file checked: /usr/lib/libgcc.a

Presumably, this means that things aren't as simple as I thought.
What am I missing?


Cheers,

Patrick

g++ (nb1 20160606) 5.4.0

$ ls /lib/libgcc*
/lib/libgcc_s.so          /lib/libgcc_s.so.1        /lib/libgcc_s.so.1.0
$ ls /usr/lib/libgcc*
/usr/lib/libgcc.a         /usr/lib/libgcc_s.so      /usr/lib/libgcc_s.so.1.0
/usr/lib/libgcc_eh.a      /usr/lib/libgcc_s.so.1

/lib/libgcc_s.so.1.0: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), 
dynamically linked, for NetBSD 7.99.31, not stripped
/usr/lib/libgcc.a: current ar archive

# Which release of libtool.m4 was used?
macro_version=2.4.2
macro_revision=1.3337
...
# The directories searched by this compiler when creating a shared library.
compiler_lib_search_dirs=""

# Dependencies to place before and after the objects being linked to
# create a shared library.
predep_objects="/usr/lib/crti.o /usr/lib/crtbeginS.o"
postdep_objects="/usr/lib/crtendS.o /usr/lib/crtn.o"
predeps=""
postdeps="-lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc"

# The library search path used internally by the compiler when linking
# a shared library.
compiler_lib_search_path=""