[LLD][COFF] Ignore /kernel flag

[pzheng]

Summary

There exists some description of the flag from Microsoft, but not sure if
there's more to it. We ignore the flag for now until we find out more about it.

https://docs.microsoft.com/en-us/cpp/build/reference/kernel-create-kernel-mode-binary?view=msvc-170

[pzheng]

minor change

[hans]

Do you have a use case for this, or have you checked that it works?

I'm not familiar with this flag, but I suspect there could be more to it (for example, do any PE headers change).

If we're not sure that this is everything that's required, I think it's better to leave the flag as unsupported.

[thieta]

I was just also about to comment that it seems like it's just ignoring the incremental flag and that it has to be more to it?

[pzheng]

Thanks for the comments, @hans and @thieta! I haven't done any verification of anything built with this flag yet. So, I am not very confident whether there's more to it than what's documented by Microsoft. I guess, for now, we'll just ignore the flag. At some point, I'll probably get a chance to do more testing on this and maybe we can revisit it then.

[pzheng]

Ignore the flag

[thieta]

Lgtm. Wait with merge until Hans checks it as well.

[pzheng]

Thanks, @thieta! @hans, please let me know if there is anything I need to address.

[hans]

lgtm

[pzheng]

Thanks!

lld/COFF/Options.td

 //==============================================================================
 
 def ignoreidl : F<"ignoreidl">;
 def ltcg : F<"ltcg">;
 def nologo : F<"nologo">;
 def throwingnew : F<"throwingnew">;
 def editandcontinue : F<"editandcontinue">;
 def fastfail : F<"fastfail">;
+def kernel : F<"kernel">;
 def pdbcompress : F<"pdbcompress">;
 
 def delay : P_priv<"delay">;
 def errorreport : P_priv<"errorreport">;
 def idlout : P_priv<"idlout">;
 def ilk : P_priv<"ilk">;
 def ltcg_opt : P_priv<"ltcg">;
 def ltcgout : P_priv<"ltcgout">;
 def maxilksize : P_priv<"maxilksize">;
 def tlbid : P_priv<"tlbid">;
 def tlbout : P_priv<"tlbout">;
 def verbose_all : P_priv<"verbose">;
 def guardsym : P_priv<"guardsym">;