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

[via llvm-commits]

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@@ -801,7 +801,7 @@ is the default, linker will not report the missing property otherwise will be re
 .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 will be reported as a warning or an error.
+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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sivan-shani wrote:

Here we like to keep the wording as it is for
```
bti-report
cet-report
```
Which are the same flag type and has the same wording. 

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