The gcompat loader compiled as a static binary doesn't work on Linux
since commit a4ff8e8620d3f4, failing with the error:

```
Uhuuh, elf segment at 0000000000400000 requested but the memory is mapped already
```

This is because the binary we are the ELF interpreter for is also loaded
at 0x400000. While it's actually okay to overlap the binary, since we're
going to call `execve` again, the kernel doesn't allow the overlap
anymore. Fix that by compiling the loader as static PIE, so it can be
loaded at a different address.

Signed-off-by: Samuel Holland <samuel@sholland.org>