Add support for the GYP_CROSSCOMPILE env var to MB.

tools/mb/mb_config.pyl

 # Copyright 2015 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.
 
 {
   # This is the list of configs that you can pass to mb; each config
   # represents a particular combination of GYP_DEFINES/gn args that
   # we must support. A given config *may* be platform-specific but
   # is not necessarily so (i.e., we might have mac, win, and linux
   # bots all using the 'gn_release_bot' config).
@@ skipping 23 matching lines @@
     'gn_debug_bot_minimal_symbols_x86': ['gn', 'debug_bot_minimal_symbols', 'x86'],
     'gn_debug_static_bot': ['gn', 'debug_static_bot'],
     'gn_linux_upload': ['gn_linux_upload'],
     'gn_release_bot': ['gn', 'release_bot'],
     'gn_release_bot_minimal_symbols': ['gn', 'release_bot_minimal_symbols'],
     'gn_release_bot_minimal_symbols_x86': ['gn', 'release_bot_minimal_symbols', 'x86'],
     'gn_release_trybot': ['gn', 'release_trybot'],
     'gn_release_trybot_x86': ['gn', 'release_trybot', 'x86'],
     'gyp_debug_bot': ['gyp', 'debug_bot'],
     'gyp_debug_bot_x86': ['gyp', 'debug_bot', 'x86'],
-    'gyp_release_bot_arm': ['gyp', 'release_bot', 'arm'],
+    'gyp_release_bot_arm': ['gyp', 'release_bot', 'arm', 'crosscompile'],
     'gyp_release_trybot': ['gyp', 'release_trybot'],
 
     # This is just for completeness; any bot that uses this config should never actually run MB.
     'none': ['none'],
 
     'swarming_asan_lsan_gyp_release_trybot': ['swarming', 'asan', 'lsan', 'release_trybot'],
     'swarming_msan_gyp_release_trybot': ['swarming', 'chromeos', 'msan', 'gyp', 'release_trybot'],
     'swarming_deterministic_gyp_release_bot': ['swarming', 'deterministic', 'gyp', 'release_bot'],
     'swarming_gpu_tests_gyp_release_trybot': ['swarming', 'gpu_tests', 'gyp', 'release_trybot'],
     'swarming_gyp_debug_bot': ['swarming', 'gyp', 'debug_bot'],
     'swarming_gyp_debug_bot_no_symbols_x86': ['swarming', 'gyp', 'debug_bot', 'no_symbols', 'x86'],
     'swarming_gyp_debug_trybot': ['swarming', 'gyp', 'debug_trybot'],
     'swarming_gyp_debug_trybot_x86': ['swarming', 'gyp', 'debug_trybot', 'x86'],
     'swarming_gyp_release_bot': ['swarming', 'gyp', 'release_bot'],
     'swarming_gyp_release_trybot': ['swarming', 'gyp', 'release_trybot'],
-    'swarming_gyp_release_trybot_arm': ['swarming', 'gyp', 'release_trybot', 'arm'],
-    'swarming_gyp_release_trybot_arm_float': ['swarming', 'gyp', 'release_trybot', 'arm_float'],
+    'swarming_gyp_release_trybot_arm': ['swarming', 'gyp', 'release_trybot', 'arm', 'crosscompile'],
+    'swarming_gyp_release_trybot_arm_float': ['swarming', 'gyp', 'release_trybot', 'arm_float', 'crosscompile'],
     'swarming_tsan_gyp_release_trybot': ['swarming', 'disable_nacl', 'tsan', 'gyp', 'release_trybot'],
 
     # clang/win doesn't work with goma yet, so this can't use debug_bot:
     'win_clang_debug_bot': ['gn', 'clang', 'debug', 'shared', 'minimal_symbols'],
   },
 
   # This is a list of configs that do not actually exist on any bot
   # but are used so commonly by devs that we must support them.
   'common_dev_configs': [
     'dev_gn_debug',
@@ skipping 52 matching lines @@
     'chromeos': {
       'gn_args': 'target_os="chromeos"',
       'gyp_defines': 'chromeos=1',
     },
 
     'clang': {
       'gn_args': 'is_clang=true',
       'gyp_defines': 'clang=1',
     },
 
+    'crosscompile': {
+      # This mixin is only needed on GYP bots that are doing cross-compiles
+      # but are *not* targetting Android or iOS (where build/gyp_chromium
+      # will set the crosscompile variable automatically). It is not need
+      # in GN at all.
+      'gyp_crosscompile': True,
+    },
+
     'dcheck_always_on': {
       'gn_args': 'dcheck_always_on=true',
       'gyp_defines': 'dcheck_always_on=1',
     },
 
     'debug': {
       'gn_args': 'is_debug=true',
       'gyp_config': 'Debug',
     },
 
@@ skipping 253 matching lines @@
       'win8_chromium_gn_rel': 'gn_release_trybot_x86',
       'win8_chromium_gn_upload': 'gn_release_bot_minimal_symbols',
       'win_clang_x64_dbg': 'win_clang_debug_bot',
     },
     'tryserver.v8': {
       'v8_linux_chromium_gn_rel': 'gn_release_trybot',
       'v8_android_chromium_gn_dbg': 'android_gn_debug_bot',
     },
   },
 }