[NFC][SmallVector] Use std::conditional_t instead of std::conditional

[yihanaa]

Summary

Use std::conditional_t instead of std::conditional

[yihanaa]

Thanks for your review @erichkeane!

llvm/include/llvm/ADT/SmallVector.h

protected:
   void set_size(size_t N) {
     assert(N <= capacity());
     Size = N;
   }
 };
 
 template <class T>
 using SmallVectorSizeType =
-    typename std::conditional<sizeof(T) < 4 && sizeof(void *) >= 8, uint64_t,
-                              uint32_t>::type;
+    std::conditional_t<sizeof(T) < 4 && sizeof(void *) >= 8, uint64_t,
+                       uint32_t>;
 
 /// Figure out the offset of the first element.
 template <class T, typename = void> struct SmallVectorAlignmentAndSize {
   alignas(SmallVectorBase<SmallVectorSizeType<T>>) char Base[sizeof(
       SmallVectorBase<SmallVectorSizeType<T>>)];
   alignas(T) char FirstEl[sizeof(T)];
 };