Use the lowest MacOS SDK available on a system

tools/gyp/xcode.gypi

 # Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 {
   'variables': {
     # Mac OS X SDK and deployment target support.
     # The SDK identifies the version of the system headers that will be used,
     # and corresponds to the MAC_OS_X_VERSION_MAX_ALLOWED compile-time macro.
     # "Maximum allowed" refers to the operating system version whose APIs are
     # available in the headers.
     # The deployment target identifies the minimum system version that the
     # built products are expected to function on.  It corresponds to the
     # MAC_OS_X_VERSION_MIN_REQUIRED compile-time macro.
     # To ensure these macros are available, #include <AvailabilityMacros.h>.
     # Additional documentation on these macros is available at
     # http://developer.apple.com/mac/library/technotes/tn2002/tn2064.html#SECTION3
     # Chrome normally builds with the Mac OS X 10.5 SDK and sets the
     # deployment target to 10.5.  Other projects, such as O3D, may override
     # these defaults.
-    'mac_sdk%': '10.5',
-    'mac_deployment_target%': '10.5',
+    'mac_sdk%': '<!(python <(DEPTH)/tools/gyp/find_mac_sdk.py 10.6)',
+    'mac_deployment_target%': '10.6',
   },
   'xcode_settings': {
     # DON'T ADD ANYTHING NEW TO THIS BLOCK UNLESS YOU REALLY REALLY NEED IT!
     # This block adds *project-wide* configuration settings to each project
     # file.  It's almost always wrong to put things here.  Specify your
     # custom xcode_settings in target_defaults to add them to targets instead.
 
     # In an Xcode Project Info window, the "Base SDK for All Configurations"
     # setting sets the SDK on a project-wide basis.  In order to get the
     # configured SDK to show properly in the Xcode UI, SDKROOT must be set
@@ skipping 14 matching lines @@
     'SYMROOT': '<(DEPTH)/xcodebuild',
 
     # It is here to make it possible to run binaries with shared libraries.
     # However, it may create problems if you move the shared library. Also,
     # this may not be appropriate for "release release" builds.
     # Perhaps we should set it to @rpath instead. See
     # http://developer.apple.com/library/mac/#documentation/DeveloperTools/Conceptual/DynamicLibraries/100-Articles/RunpathDependentLibraries.html#//apple_ref/doc/uid/TP40008306-SW1
     'INSTALL_PATH': '$(TARGET_BUILD_DIR)',
   },
 }