Octave forge packages installation - octave

Question

I'm trying to install image-2.6.1 package to GNU Octave, version 4.0.0. I downloaded image-2.6.1.tar.gz and tried to install it with
pkg install /home/vladimirmatveev/Downloads/image-2.6.1.tar.gz
but get an error.
configure: error: in `/tmp/oct-BAtlFb/image-2.6.1/src':
configure: error: C++ compiler cannot create executables
See `config.log' for more details
checking for a sed that does not truncate output... /bin/sed
checking for octave... /usr/bin/octave
checking for mkoctfile... /usr/bin/mkoctfile
checking whether the C++ compiler works... no
pkg: error running the configure script for image.
error: called from 'configure_make' in file /usr/share/octave/4.0.0/m/pkg/private/configure_make.m near line 79, column 9
I am sure I have C/C++ compilers, they are gcc and g++ (when I am trying to install them with apt-get it says I already have a newest version and I am sure it is true).
I tried to set c/c++ compilers to system variables with
export CC=/usr/bin/gcc-4.8
export CXX=/usr/bin/g++-4.8
or
export CC=/usr/bin/gcc-5
export CXX=/usr/bin/g++-5
(I have both versions) but it didn't helped. It usually works for me when cmake can not find a compiler.
I found im-config.log file, but it contains only
Script for ibus started at run_im.
Script for auto started at run_im.
Script for default started at run_im.
I am not sure this is that config file which was mentioned in error message, but it is the only file which has suitable modification date.
I am working at ubuntu 16.04.
I unpackaged .tar.gz, cd to it and to src/, then run ./configure and there was no troubles found while checking compiler, here is the console log.
checking for a sed that does not truncate output... /bin/sed
checking for octave... /usr/bin/octave
checking for mkoctfile... /usr/bin/mkoctfile
checking whether the C++ compiler works... yes
checking for C++ compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C++ compiler... yes
checking whether /usr/bin/g++-5 accepts -g... yes
checking for /usr/bin/g++-5 option to enable C++11 features... -std=gnu++11
checking whether xmin is in the octave::math namespace... no
checking whether templated lambda functions accept '&const int'... yes
configure: creating ./config.status
config.status: creating im2double.m
config.status: creating Makefile
config.status: creating config.h
Here is full config log http://pastebin.com/u6MNSqCB