extconf.rb in annoy-rb-0.2.0

- old
+ new

@@ -1,9 +1,9 @@
 require 'mkmf'
 
 abort 'libstdc++ is not found.' unless have_library('stdc++')
 
-$CXXFLAGS << " -march=native"
+$CXXFLAGS << " -std=c++14 -march=native -DANNOYLIB_MULTITHREADED_BUILD"
 $INCFLAGS << " -I$(srcdir)/src"
 $VPATH << "$(srcdir)/src"
 
 create_makefile('annoy/annoy')