[libunwind] [libunwind][NFC] Typo fixes & comments corrections & code style changes. (PR #174565)

[Benjamin Maxwell via cfe-commits]

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@@ -120,10 +120,10 @@ typedef int (*unw_find_dynamic_unwind_sections)(
 extern int __unw_add_find_dynamic_unwind_sections(
     unw_find_dynamic_unwind_sections find_dynamic_unwind_sections);
 
-// Deregister a dynacim unwind-info lookup callback.
+// Deregister a dynamic unwind-info lookup callback.
 //
 // Returns UNW_ESUCCESS for successful deregistrations. If the given callback
-// has already been registered then UNW_EINVAL will be returned.
+// does not present then UNW_EINVAL will be returned.
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MacDue wrote:

`does not present` is not the correct wording. It should be `If the given callback is not present then UNW_EINVAL will be returned.`

https://github.com/llvm/llvm-project/pull/174565