To use shared libraries need LD_LIBRARY_PATH defined with the location of the shared library and having the shared library in the path when compiling

with csh/tcsh:
setenv LD_LIBRARY_PATH $LD_LIBRARY_PATH':.'
with sh/bash:
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH':.'

Note that now hsared libraries are added to the sub_libs folders, next to the .a libraries. Thus when compiling the program test, it assumes it uses a shared library and you might get:

./interpostest_f90 > /tmp/osauter/toto
./interpostest_f90: error while loading shared libraries: libinterposgfortran.so: cannot open shared object file: No such file or directory

This is resolved by:
setenv LD_LIBRARY_PATH $LD_LIBRARY_PATH':'$HOME'/interpos_develop/interpos_libs/gfortran_libs'
(or in sh/bash: export LD_LIBRARY_PATH=$LD_LIBRARY_PATH':'$HOME'/interpos_develop/interpos_libs/gfortran_libs' )
./interpostest_f90 > /tmp/osauter/toto.m