hardware: rename none optimization flags to dunno

Library/Homebrew/extend/os/linux/extend/ENV/shared.rb

@@ -10,7 +10,7 @@ module SharedEnvExtension
     elsif Hardware::CPU.intel? || Hardware::CPU.arm?
       :native
     else
-      :none
+      :dunno
     end
   end
 end

Library/Homebrew/hardware.rb

@@ -27,7 +27,7 @@ module Hardware
       sig { returns(T::Hash[Symbol, String]) }
       def optimization_flags
         @optimization_flags ||= T.let({
-          none:               "",
+          dunno:              "",
           native:             arch_flag("native"),
           ivybridge:          "-march=ivybridge",
           sandybridge:        "-march=sandybridge",