[compiler] Fix -Wshadow

Bug: v8:12244,v8:12245
Change-Id: Ibef9eaa7f1c3a58ef290b61a9f46b98fc30184af
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3274019Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77852}

src/compiler/diamond.h

@@ -39,8 +39,8 @@ struct Diamond {
   void Chain(Node* that) { branch->ReplaceInput(1, that); }
 
   // Nest {this} into either the if_true or if_false branch of {that}.
-  void Nest(Diamond const& that, bool if_true) {
-    if (if_true) {
+  void Nest(Diamond const& that, bool cond) {
+    if (cond) {
       branch->ReplaceInput(1, that.if_true);
       that.merge->ReplaceInput(0, merge);
     } else {