[flang] Support -f(no)-inline-functions

Before #218533, a warning would be emitted if this option was used.

```
flang-22: warning: optimization flag '-fkeep-inline-functions' is not supported [-Wignored-optimization-argument]
```

After #218533, flang will fail with an unknown option error. This option is good to have when debugging optimized code and for compatibility with clang.

Start by tracing flang's handling of the -f(no)-inline-functions options and compare it with the prior warning behavior described in the issue. Add support so these options are accepted for debugging and clang compatibility without producing an unknown-option error, then verify the relevant flang option tests or command-line behavior.

Written by the indexing model from the issue text.