[clang-tidy] ElseAfterReturn check wont suggest fixes if preprocessor branches are involved

Consider this code:
```
if (Cond) {
#ifdef X_SUPPORTED
  X();
#else
  return;
#endif
} else {
  Y();
}
Z();```

In this example, if `X_SUPPORTED` is not defined, currently we'll get a warning from the else-after-return check. However If we apply that fix, and then the code is recompiled with `X_SUPPORTED` defined, we have inadvertently changed the behaviour of the if statement due to the else being removed. Code flow when `Cond` is `true` will be:
```
X();
Y();
Z();```
 where as before the fix it was:
 ```
 X();
 Z();```

 This patch adds checks that guard against `#endif` directives appearing between the control flow interrupter and the else and not applying the fix if they are detected.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D91485