Freeze optimization flags hash rather than duping it

Library/Homebrew/os/linux/hardware.rb

@@ -1,6 +1,6 @@
 module LinuxCPUs
-  OPTIMIZATION_FLAGS = {}
-  def optimization_flags; OPTIMIZATION_FLAGS.dup; end
+  OPTIMIZATION_FLAGS = {}.freeze
+  def optimization_flags; OPTIMIZATION_FLAGS; end
 
   def type
     @cpu_type ||= case `uname -m`

Library/Homebrew/os/mac/hardware.rb

@@ -7,8 +7,8 @@ module MacCPUs
     :g4 => '-mcpu=7400',
     :g4e => '-mcpu=7450',
     :g5 => '-mcpu=970'
-  }
-  def optimization_flags; OPTIMIZATION_FLAGS.dup; end
+  }.freeze
+  def optimization_flags; OPTIMIZATION_FLAGS; end
 
   # These methods use info spewed out by sysctl.
   # Look in <mach/machine.h> for decoding info.