[lld] [LLD][Docs] Document -z gcs= option in the man page (PR #146522)

[Peter Smith via llvm-commits]

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@@ -798,6 +798,11 @@ Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_IBT or GNU_PROPERTY
 .Cm none
 is the default, linker will not report the missing property otherwise will be reported as a warning or an error.
 .Pp
+.It Cm gcs-report Ns = Ns Ar [none|warning|error]
+Specify how to report missing GNU_PROPERTY_AARCH64_FEATURE_1_GCS property. GNU_PROPERTY_AARCH64_FEATURE_1_GCS indicates object file support for the Guarded Control Stack security feature.
+.Cm none
+is the (default) linker will not report the missing property otherwise, missing property will be reported as a warning or an error.
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smithp35 wrote:

Apologies for being a pain. A couple of nits on this line: 

I meant (default) at the start of the line. However, looking at bti-report and cet-report above it is probably better to follow the convention and use "is the default," . It was probably that originally; sorry for the noise.

The comma after otherwise looks to be in the wrong position [1]. I think we should follow the wording of bit-report and cet-report.
```
is the default, linker will not report the missing property otherwise will be reported as a warning or an error.
```
[1] If I were rewriting with a comma I'd say "report the missing propery, otherwise it will be reported as a warning or an error." However best to stay consistent with the existing wording.

https://github.com/llvm/llvm-project/pull/146522