On Thinlinc and the compute hosts, several gcc Compiler versions are installed plus the Ubuntu default gcc.
By default, the Ubuntu gcc is used.
To use another on, type gcc- and hit 'enter' two times - you will see all installed 'gcc-' versions (incl. the version number in the program name).
A nice explanation of compiler / linker behaviour: https://homepages.inf.ed.ac.uk/imurray2/compnotes/library_linking.txt