[x86] Disable AVX unless the operating system explicitly claims to support it.

src/base/cpu.h

Index: src/base/cpu.h
diff --git a/src/base/cpu.h b/src/base/cpu.h
index 193ea5a921b0e7d78d9d71f29c97571bc6f8b35a..e8a6c8ea267b899c16eee7675bc4e17a7b208721 100644
--- a/src/base/cpu.h
+++ b/src/base/cpu.h
@@ -83,6 +83,7 @@ class CPU FINAL {
   bool has_ssse3() const { return has_ssse3_; }
   bool has_sse41() const { return has_sse41_; }
   bool has_sse42() const { return has_sse42_; }
+  bool has_osxsave() const { return has_osxsave_; }
   bool has_avx() const { return has_avx_; }
   bool has_fma3() const { return has_fma3_; }
   bool is_atom() const { return is_atom_; }
@@ -121,6 +122,7 @@ class CPU FINAL {
   bool has_sse41_;
   bool has_sse42_;
   bool is_atom_;
+  bool has_osxsave_;
   bool has_avx_;
   bool has_fma3_;
   bool has_idiva_;