Make gyp autodetection of host_arch work for 64-bit kernel and 32-bit userland

build/common.gypi

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 85 matching lines @@
             ['(OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris") and chromeos==0', {
               'desktop_linux%': 1,
             }, {
               'desktop_linux%': 0,
             }],
 
             # Compute the architecture that we're building on.
             ['OS=="win" or OS=="mac" or OS=="ios"', {
               'host_arch%': 'ia32',
             }, {
-              # This handles the Unix platforms for which there is some support.
-              # Anything else gets passed through, which probably won't work
-              # very well; such hosts should pass an explicit target_arch to
-              # gyp.
-              'host_arch%':
-                '<!(uname -m | sed -e "s/i.86/ia32/;s/x86_64/x64/;s/amd64/x64/;s/arm.*/arm/;s/i86pc/ia32/")',
+              'host_arch%': '<!(python <(DEPTH)/build/linux/detect_host_arch.py)',
             }],
 
             # Embedded implies ozone.
             ['embedded==1', {
               'use_ozone%': 1,
             }],
 
             ['embedded==1', {
               'use_system_fontconfig%': 0,
             }, {
@@ skipping 4763 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }