Possible runtime bug in preprocessing of command line arguments passed to the D main

[Basile B.]

The following code, on linux

```d
module runnable;
​
extern(C) int execv(const char* p, const char** args);
​
immutable src = `
     import std.getopt;
     void main(string[] args)
     {
         bool c;
         getopt(args, "c", &c);
     }
`;
​
void prepareProgram()
{
     import std.process  : execute;
     import std.file     : write;
     write("a.d", src);
     execute(["dmd", "a.d"]);
}
​
void main(string[] args)
{
     prepareProgram();
     execv("a", null);
}
```

results in a std.getopt exception:

> object.Exception@/usr/include/dmd/phobos/std/getopt.d(423): 
> Invalid arguments string passed: program name missing

Context is a program not written in D that uses execv to call a D 
program that uses getopt.

What do you think ?