Use ATTRIBUTE_UNUSED more.

Use it in lieu of UNUSED(), which had some incorrect uses.

Change-Id: If247dce58b72056f6eea84968e7196f0b5bef4da
diff --git a/compiler/compiler.h b/compiler/compiler.h
index 9b4dbe0..8788dc1 100644
--- a/compiler/compiler.h
+++ b/compiler/compiler.h
@@ -77,9 +77,8 @@
    * information.
    * @note This is used for backtrace information in generated code.
    */
-  virtual std::vector<uint8_t>* GetCallFrameInformationInitialization(const CompilerDriver& driver)
-      const {
-    UNUSED(driver);
+  virtual std::vector<uint8_t>* GetCallFrameInformationInitialization(
+      const CompilerDriver& driver ATTRIBUTE_UNUSED) const {
     return nullptr;
   }