Function overhead

In 0.14.0, the function overhead appeared. For example, a function that returns its argument produces:

```asm
push    rbp         ; why do we need that?!
mov     rbp, rsp    ; ?!?
mov     eax, edi
pop     rbp         ; ?!?
ret
```

The correct assembly was in 0.13.0:

```asm
mov     eax, edi
ret
```

https://godbolt.org/z/9z1d5hsoK