[llvm] [Support] Fix unused variable warning in `reserveExtraSpace`; NFC (PR #106327)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-support

Author: None (goldsteinn)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/106327.diff


1 Files Affected:

- (modified) llvm/include/llvm/Support/raw_ostream.h (+1-1) 


``````````diff
diff --git a/llvm/include/llvm/Support/raw_ostream.h b/llvm/include/llvm/Support/raw_ostream.h
index df9ee2e5a78586..2570c826502e7c 100644
--- a/llvm/include/llvm/Support/raw_ostream.h
+++ b/llvm/include/llvm/Support/raw_ostream.h
@@ -157,7 +157,7 @@ class raw_ostream {
   /// So that the stream could keep at least tell() + ExtraSize bytes
   /// without re-allocations. reserveExtraSpace() does not change
   /// the size/data of the stream.
-  virtual void reserveExtraSpace(uint64_t ExtraSize) {}
+  virtual void reserveExtraSpace(uint64_t ExtraSize) { (void)ExtraSize; }
 
   /// Set the stream to be buffered, with an automatically determined buffer
   /// size.

``````````

</details>


https://github.com/llvm/llvm-project/pull/106327