Example input:

---------- t.c ---------
int something();                                                                 
                                                                                 
int f(int arg) {                                                                 
 return 0;                                                                       
 (void)(false ? 1 : something());                                                
}   
-----------------------

$ c++ -c t.cc -finstrument-functions -Wall -Werror
t.cc: In function ‘int f(int)’:
t.cc:6:1: error: control reaches end of non-void function [-Werror=return-type]
 }
 ^
$ echo $?
1
$

But:

$ c++ -c t.cc -Wall -Werror
$ echo $?
0
$