Only require SSE2 at minimum hardware requirement.

runtime/vm/assembler_x64.cc

Index: runtime/vm/assembler_x64.cc
===================================================================
--- runtime/vm/assembler_x64.cc	(revision 15244)
+++ runtime/vm/assembler_x64.cc	(working copy)
@@ -19,18 +19,11 @@
 DEFINE_FLAG(bool, use_sse41, true, "Use SSE 4.1 if available");
 
 
-bool CPUFeatures::sse3_supported_ = false;
 bool CPUFeatures::sse4_1_supported_ = false;
 #ifdef DEBUG
 bool CPUFeatures::initialized_ = false;
 #endif
 
-bool CPUFeatures::sse3_supported() {
-  DEBUG_ASSERT(initialized_);
-  return sse3_supported_;
-}
-
-
 bool CPUFeatures::sse4_1_supported() {
   DEBUG_ASSERT(initialized_);
   return sse4_1_supported_ && FLAG_use_sse41;
@@ -63,7 +56,6 @@
   typedef uint64_t (*DetectCPUFeatures)();
   uint64_t features =
       reinterpret_cast<DetectCPUFeatures>(instructions.EntryPoint())();
-  sse3_supported_ = (features & kSSE3BitMask) != 0;
   sse4_1_supported_ = (features & kSSE4_1BitMask) != 0;
 #ifdef DEBUG
   initialized_ = true;