all-missed-specializations doesn't suggest warning
`-Weverything` turns on `-Wall-missed-specializations`. When most warnings print, they say, e.g.,
`warning: [-Wincomplete-uni-patterns]`
which is helpful because I can then easily suppress all warnings of that type with an `-fno-warn-*`. But missed specializations do not show the warning flag:
```
Foo.hs: warning:
Could not specialise imported function `foo'
Probable fix: add INLINABLE pragma on `foo'
```
There is no indication of what warning flag triggered the warning.
<details><summary>Trac metadata</summary>
| Trac field | Value |
| ---------------------- | ------------ |
| Version | 8.6.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | low |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture | |
</details>
<!-- {"blocked_by":[],"summary":"all-missed-specializations doesn't suggest warning","status":"New","operating_system":"","component":"Compiler","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"8.6.3","keywords":[],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"Bug","description":"`-Weverything` turns on `-Wall-missed-specializations`. When most warnings print, they say, e.g.,\r\n\r\n`warning: [-Wincomplete-uni-patterns]`\r\n\r\nwhich is helpful because I can then easily suppress all warnings of that type with an `-fno-warn-*`. But missed specializations do not show the warning flag:\r\n\r\n{{{\r\nFoo.hs: warning:\r\n Could not specialise imported function `foo'\r\n Probable fix: add INLINABLE pragma on `foo'\r\n}}}\r\n\r\nThere is no indication of what warning flag triggered the warning.","type_of_failure":"OtherFailure","blocking":[]} -->
issue