Make `GetGccVersion()` method return a tuple instead of a list.  This fixes the `GccOptNative` builds.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19092 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2370 dox

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19093 b5f69653-2bf5-0310-8201-b0dafb8e1405