[llvm] [llvm-objcopy] Improve help messages (PR #82830)

[James Henderson via llvm-commits]

================
@@ -39,13 +42,13 @@ def p : Flag<["-"], "p">,
         HelpText<"Alias for --preserve-dates">;
 
 def strip_all : Flag<["--"], "strip-all">,
-                HelpText<"Remove non-allocated sections outside segments. "
-                         ".gnu.warning* and .ARM.attribute sections are not "
-                         "removed">;
+    HelpText<"For ELF, remove all symbols and non-alloc sections not "
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jh7370 wrote:

```suggestion
    HelpText<"For ELF, remove all symbols and non-alloc sections not within "
```

https://github.com/llvm/llvm-project/pull/82830