Can't legalize widths between legal widths.

Repro `-O1`
```
long a;char b;void c(void){a=0;for(;a!=4;++a){a||(b=0);}}
```
---
Since that doesn't repro anymore, here's a direct repro:
```
target triple = "ez80"
define i9 @test() {
  ret i9 0
}
```
---
C repro `-O0`:
```
struct { int : 18, a : 15; } b; c() { return b.a; }
```