Increase to 5 the number of parameters to execv icecc-create-env

* Actually the min size of argv var is 4 but it must be 5:
   argv = [icecc-create-env, --gcc, /usr/bin/gcc, /usr/bin/g++, NULL]

Signed-off-by: Ragner Magalhaes <ragner.magalhaes@gmail.com>