Split the GN 'snapshot_toolchain' logic out into an include file.

snapshot_toolchain.gni

-# Copyright 2013 the V8 project authors. All rights reserved.
+# Copyright 2015 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
 #       with the distribution.
 #     * Neither the name of Google Inc. nor the names of its
 #       contributors may be used to endorse or promote products derived
 #       from this software without specific prior written permission.
 #
 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-# Watchlist Rules
-# Refer: http://dev.chromium.org/developers/contributing-code/watchlists
+# The snapshot needs to be compiled for the host, but compiled with
+# a toolchain that matches the bit-width of the target.
 
-# IMPORTANT: The regular expression filepath is tested against each path using
-# re.search, so it is not usually necessary to add .*.
+# TODO(GYP): For now we only support 32-bit little-endian target builds from an
+# x64 Linux host. Eventually we need to support all of the host/target
+# configurations v8 runs on.
+if (host_cpu == "x64" && host_os == "linux") {
+  if (target_cpu == "arm" || target_cpu == "mipsel" || target_cpu == "x86") {
+    snapshot_toolchain = "//build/toolchain/linux:clang_x86"
+  } else if (target_cpu == "x64") {
+    snapshot_toolchain = "//build/toolchain/linux:clang_x64"
+  } else {
+    assert(false, "Need environment for this arch")
+  }
+} else {
+  snapshot_toolchain = default_toolchain
+}
 
-{
-  'WATCHLIST_DEFINITIONS': {
-    'public_api': {
-      'filepath': 'include/',
-    },
-    'snapshot': {
-      'filepath': 'src/snapshot/',
-    },
-    'debugger': {
-      'filepath': 'src/debug/',
-    },
-  },
 
-  'WATCHLISTS': {
-    'public_api': [
-      'phajdan.jr@chromium.org',
-    ],
-    'snapshot': [
-      'yangguo@chromium.org',
-    ],
-    'debugger': [
-      'yangguo@chromium.org',
-    ],
-  },
-}