Fix an instance of -Wunused-but-set-variable.

Bug: chromium:794619
Change-Id: I335291b8ea7a326abbf66df535d3fa98aff9e4fc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3206277
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77239}

src/builtins/arm/builtins-arm.cc

@@ -670,6 +670,7 @@ void Generate_JSEntryVariant(MacroAssembler* masm, StackFrame::Type type,
   Handle<Code> trampoline_code =
       masm->isolate()->builtins()->code_handle(entry_trampoline);
   DCHECK_EQ(kPushedStackSpace, pushed_stack_space);
+  USE(pushed_stack_space);
   __ Call(trampoline_code, RelocInfo::CODE_TARGET);
 
   // Unlink this frame from the handler chain.