build: Add build flag "-Wunused-variable"
In order to detect cases of unused variables, it would be useful to build ns-3 with the flag -Wunused-variable. This allows enforcing the coding style rule about unused variables.
In order to detect cases of unused variables, it would be useful to build ns-3 with the flag -Wunused-variable. This allows enforcing the coding style rule about unused variables.