_mm256_blendv_epi8 needs avx2

Change-Id: Ib10215e1e5a86bf78cc34f9dca670417bb217b73
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/317271
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/include/private/SkVx.h b/include/private/SkVx.h
index 9d8f773..0455550 100644
--- a/include/private/SkVx.h
+++ b/include/private/SkVx.h
@@ -354,7 +354,7 @@
 SINT Vec<N,T> if_then_else(const Vec<N,M<T>>& cond, const Vec<N,T>& t, const Vec<N,T>& e) {
     // Specializations inline here so they can generalize what types the apply to.
     // (This header is used in C++14 contexts, so we have to kind of fake constexpr if.)
-#if defined(__AVX__)
+#if defined(__AVX2__)
     if /*constexpr*/ (N*sizeof(T) == 32) {
         return unchecked_bit_pun<Vec<N,T>>(_mm256_blendv_epi8(unchecked_bit_pun<__m256i>(e),
                                                               unchecked_bit_pun<__m256i>(t),