[clang] [Driver] Restrict Ofast deprecation help message to Clang (PR #101682)

[Aaron Ballman via cfe-commits]

================
@@ -932,8 +932,9 @@ def O_flag : Flag<["-"], "O">, Visibility<[ClangOption, CC1Option, FC1Option]>,
   Alias<O>, AliasArgs<["1"]>;
 def Ofast : Joined<["-"], "Ofast">, Group<O_Group>,
   Visibility<[ClangOption, CC1Option, FlangOption]>,
-  HelpText<"Deprecated; use '-O3 -ffast-math' for the same behavior,"
-  " or '-O3' to enable only conforming optimizations">;
+  HelpTextForVariants<[ClangOption,CC1Option],
----------------
AaronBallman wrote:

```suggestion
  HelpTextForVariants<[ClangOption, CC1Option],
```

https://github.com/llvm/llvm-project/pull/101682