Fix linphonesdk_dependent_option() behavior
Prevent linphonesdk_dependent_option() to redefine the variable related to the option if it has already been defined as local or cache variable. Compliance with CMP0077.
Edited by François Grisez
Prevent linphonesdk_dependent_option() to redefine the variable related to the option if it has already been defined as local or cache variable. Compliance with CMP0077.