Fix --build-bottle CFLAGS.

The CFLAGS were previously not generic enough.

References Homebrew/homebrew#18944.
References Homebrew/homebrew#19179.

Library/ENV/4.3/cc

@@ -148,17 +148,22 @@ class Cmd
     args
   end
   def cflags
-    if cccfg? 'Ob'
-      %w{-mtune=generic -Oz}
-    elsif cccfg? 'O'
+    return [] unless cccfg? 'O'
+
     args = %w{-pipe -w -Os}
+
+    # When bottling use the oldest supported CPU type.
+    if cccfg? 'bi6'
+      args << '-march=core2'
+    elsif cccfg? 'bi'
+      args << '-march=prescott'
+    else
       args << '-march=native' if tool =~ /clang/
+    end
+
     args += %w{-arch i386 -arch x86_64} if cccfg? 'u'
     args << "-std=#{@arg0}" if @arg0 =~ /c[89]9/
     args
-    else
-      []
-    end
   end
   def syslibpath
     # We reject brew's lib as we explicitly add this as a -L flag, thus it

Library/Homebrew/extend/ENV.rb

@@ -326,7 +326,7 @@ module HomebrewEnvExtension
     append flags, xarch unless xarch.empty?
 
     if ARGV.build_bottle?
-      append flags, '-mtune=generic'
+      append flags, Hardware::CPU.optimization_flags[MacOS.oldest_cpu]
     else
       # Don't set -msse3 and older flags because -march does that for us
       append flags, map.fetch(Hardware::CPU.family, default)

Library/Homebrew/macos.rb

@@ -34,6 +34,18 @@ module MacOS extend self
     cat.to_s.gsub('_', '').to_sym
   end
 
+  def oldest_cpu
+    if Hardware::CPU.type == :intel
+      if Hardware::CPU.is_64_bit?
+        :core2
+      else
+        :core
+      end
+    else
+      Hardware::CPU.family
+    end
+  end
+
   def locate tool
     # Don't call tools (cc, make, strip, etc.) directly!
     # Give the name of the binary you look for as a string to this method

Library/Homebrew/superenv.rb

@@ -182,7 +182,17 @@ class << ENV
 
   def determine_cccfg
     s = ""
-    s << 'b' if ARGV.build_bottle?
+    if ARGV.build_bottle?
+      s << if Hardware::CPU.type == :intel
+        if Hardware::CPU.is_64_bit?
+          'bi6'
+        else
+          'bi'
+        end
+      else
+        'b'
+      end
+    end
     # Fix issue with sed barfing on unicode characters on Mountain Lion
     s << 's' if MacOS.version >= :mountain_lion
     # Fix issue with 10.8 apr-1-config having broken paths