No "Unreachable code" warning on a static falsy conditional expression
FPC from trunk
```pascal
program project1;
var
a: byte;
begin
if 1 > 2 then
a := 0; // <= no warning
if False then
a := 0; // <= project1.lpr(8,5) Warning: Unreachable code
Writeln(a);
end.
```
issue