Fix unused variable on win32 build

src/base/platform/platform.h

Index: src/base/platform/platform.h
diff --git a/src/base/platform/platform.h b/src/base/platform/platform.h
index 018d9e7a9c74ca203bd6de7c44a530dcf7ded276..9259ec8f78e13247c6536389346e08186cdc5824 100644
--- a/src/base/platform/platform.h
+++ b/src/base/platform/platform.h
@@ -56,6 +56,7 @@ inline intptr_t InternalGetExistingThreadLocal(intptr_t index) {
   const intptr_t kMaxSlots = kMaxInlineSlots + 1024;
   const intptr_t kPointerSize = sizeof(void*);
   DCHECK(0 <= index && index < kMaxSlots);
+  USE(kMaxSlots);
   if (index < kMaxInlineSlots) {
     return static_cast<intptr_t>(__readfsdword(kTibInlineTlsOffset +
                                                kPointerSize * index));