After a Linux (Mint) upgrade
  some libraries could not be found /
   / were not correctly handled in the upgrade /
   / suffered from a break+resume in the process:

/usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16 - not found
/usr/lib/x86_64-linux-gnu/libstdc++.so.6 - its symlink

Although the files existed, they could not be located correctly before the packages shown in the table below were re-installed
apt-get install ia32-libs
etc. , all five packages. 

Here's the relevant section of what Absoft wrote about installing compiler on 64-bit platforms
 
Ubuntu 12.04

Ubuntu 13.04


A default installation of Ubuntu 12.04 or 13.04 requires the following additional software to fully support Absoft Fortran 2014:

Package                            Description
----------------------       ---------------------------------------
ia32-libs                    Support for running 32 bit programs
gcc                          Support for software development
g++                          Support for software development
gcc-multilib                 Support for building 32 bit programs
g++-multilib                 Support for building 32 bit programs


Examples below give a possible error messages reported when a package is missing and the apt-get command to install the package.

1) Compiler front-end fails to load, no 32 bit executable support

   Symptom:

     $ af90 t.f
       sh: /opt/absoft14.0/bin/af90fe64: not found

   Fix: install 32 bit executable support

     $ sudo apt-get install ia32-libs

   Alternate Fix: install minimum 32 bit executable support

     $ sudo apt-get install libc6-i386
     $ sudo apt-get install lib32stdc++6

2) Link fails, g++ not found

   Symptom:

    $ af90 t.f
    sh: g++: not found
    link failed.

   Fix: install g++ (along with other C development tools)

    $ sudo apt-get install g++

3) Building 32 bit program fails

    Symptom:

     $ af90 -m32 t.f
       /usr/bin/ld: cannot find crt1.o: No such file or directory
       /usr/bin/ld: cannot find crti.o: No such file or directory
       /usr/bin/ld: cannot find -lpthread

    Fix: install 32 bit development support

     $ sudo apt-get install gcc-multilib