stdenv: use Xcode SDK on PPC

The system libraries won't have an Intel slice on this platform.

Library/Homebrew/extend/ENV/std.rb

@@ -200,7 +200,7 @@ module Stdenv
     self["CPATH"] = "#{HOMEBREW_PREFIX}/include"
     prepend "LDFLAGS", "-L#{HOMEBREW_PREFIX}/lib"
 
-    if (sdk = MacOS.sdk_path(version)) && !MacOS::CLT.installed?
+    if (sdk = MacOS.sdk_path(version)) && !MacOS::CLT.installed? || Hardware::CPU.ppc?
       # Extra setup to support Xcode 4.3+ without CLT.
       self["SDKROOT"] = sdk
       # Tell clang/gcc where system include's are:

Library/Homebrew/os/mac.rb

@@ -80,6 +80,8 @@ module OS
         opts << "#{Xcode.prefix}/Platforms/MacOSX.platform/Developer/SDKs/MacOSX#{v}.sdk"
         # Xcode < 4.3 style
         opts << "/Developer/SDKs/MacOSX#{v}.sdk"
+        # Tiger-style
+        opts << "/Developer/SDKs/MacOSX#{v}u.sdk"
         @sdk_path[key] = opts.map { |a| Pathname.new(a) }.detect(&:directory?)
       end
     end