Fix cpu-info/cpp-defines mismatch.

Rationale:
__POPCNT__ is the right way to cpp-test for popcnt support

Change-Id: I3dac215f862701e04519e89ca97c159b1e4385c8
diff --git a/runtime/arch/x86/instruction_set_features_x86.cc b/runtime/arch/x86/instruction_set_features_x86.cc
index da01ee4..b97a8db 100644
--- a/runtime/arch/x86/instruction_set_features_x86.cc
+++ b/runtime/arch/x86/instruction_set_features_x86.cc
@@ -150,8 +150,11 @@
   // No #define for memory synchronization preference.
   const bool prefers_locked_add = false;
 
-  // No #define for popcnt.
+#ifndef __POPCNT__
   const bool has_POPCNT = false;
+#else
+  const bool has_POPCNT = true;
+#endif
 
   if (x86_64) {
     return new X86_64InstructionSetFeatures(smp, has_SSSE3, has_SSE4_1, has_SSE4_2, has_AVX,