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

[Daniel Kiss via llvm-commits]

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@@ -959,13 +959,13 @@ disallows overlap.
 x86 only, use shadow stack.
 .Pp
 .It Cm gcs Ns = Ns Ar [implicit|never|always]
-Specify how the GCS bit is set. A set GCS bit indicates that the object file supports the Guarded Control Stack security feature.
+Specifies how the GNU_PROPERTY_AARCH64_FEATURE_1_GCS bit is set in the output ELF file. When set, it indicates support for the Guarded Control Stack (GCS) security feature.
 .Cm implicit
-is the default, where the GCS bit is inferred from the input objects.
+is the (default) GCS feature bit is inferred from the input object marking.
 .Cm never
-disables the GCS bit regardless of input markings.
+clears the GCS feature bit regardless of input object markings.
 .Cm always
-enables the GCS bit regardless of input markings.
+set the GCS feature bit regardless of input object markings.
----------------
DanielKristofKiss wrote:

```suggestion
sets the GCS feature bit regardless of input object markings.
```

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