Add options the modify the state of the executable flag of the GNU_STACK
program header. That header indicates whether the object is requiring an
executable stack.
Fix off by one error in the code that reads interpreter from the ELF
file. This was not evident when it was written directly to STDOUT but
became problematic through my exploration of new functionality (#357)
since there was an additional '\0' and the strings would not concatenate
as a result.
Christian Göttsche