Rollup merge of #153043 - RalfJung:c-flag-missing, r=lqd

fix error on missing value for -C flags

Before:
```
error: codegen option `panic` requires either `unwind`, `abort`, or `immediate-abort` (C panic=<value>)
```
After:
```
error: codegen option `panic` requires either `unwind`, `abort`, or `immediate-abort` (`-C panic=<value>`)
```

The second commit renames a field in the options macro for better consistency; that did not seem worth its own PR.

Author: JonathanBrouwer