determine_optflags: Default is -march=native

Library/Homebrew/extend/ENV/std.rb

@@ -7,7 +7,7 @@ module Stdenv
 
   # @private
   SAFE_CFLAGS_FLAGS = "-w -pipe".freeze
-  DEFAULT_FLAGS = "-march=core2 -msse4".freeze
+  DEFAULT_FLAGS = "-march=native".freeze
 
   # @private
   def setup_build_environment(formula = nil)
@@ -108,7 +108,7 @@ module Stdenv
 
   def gcc_4_2
     super
-    set_cpu_cflags
+    set_cpu_cflags "-march=core2 -msse4"
   end
 
   GNU_GCC_VERSIONS.each do |n|
@@ -124,7 +124,7 @@ module Stdenv
     # Clang mistakenly enables AES-NI on plain Nehalem
     map = Hardware::CPU.optimization_flags
     map = map.merge(nehalem: "-march=native -Xclang -target-feature -Xclang -aes")
-    set_cpu_cflags "-march=native", map
+    set_cpu_cflags DEFAULT_FLAGS, map
   end
 
   def minimal_optimization

Library/Homebrew/extend/ENV/super.rb

@@ -235,7 +235,7 @@ module Superenv
       Hardware::CPU.optimization_flags.fetch(arch)
     elsif Hardware::CPU.intel? && !Hardware::CPU.sse4?
       Hardware::CPU.optimization_flags.fetch(Hardware.oldest_cpu)
-    elsif compiler == :clang
+    elsif ![:gcc_4_0, :gcc_4_2].include?(compiler)
       "-march=native"
     # This is mutated elsewhere, so return an empty string in this case
     else

Library/Homebrew/hardware.rb

@@ -11,7 +11,6 @@ module Hardware
         core: "-march=prescott",
         armv6: "-march=armv6",
         armv8: "-march=armv8-a",
-        dunno: "-march=native",
       }.freeze
 
       def optimization_flags