Make it possible to compile ICU both with the host and target toolset.

icu.gyp

 # 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.
 
 {
   'variables': {
     'use_system_icu%': 0,
     'icu_use_data_file_flag%': 0,
+    'want_separate_host_toolset%': 0,
   },
   'target_defaults': {
     'direct_dependent_settings': {
       'defines': [
         # Tell ICU to not insert |using namespace icu;| into its headers,
         # so that chrome's source explicitly has to use |icu::|.
         'U_USING_ICU_NAMESPACE=0',
       ],
     },
+    'defines': [
+      'U_USING_ICU_NAMESPACE=0',
+    ],
+    'conditions': [
+      ['component=="static_library"', {
+        'defines': [
+          'U_STATIC_IMPLEMENTATION',
+        ],
+      }],
+    ],
+    'include_dirs': [
+      'source/common',
+      'source/i18n',
+    ],
+    'msvs_disabled_warnings': [4005, 4068, 4355, 4996, 4267],
   },
   'conditions': [
-    ['use_system_icu==0', {
-      'target_defaults': {
-        'defines': [
-          'U_USING_ICU_NAMESPACE=0',
-        ],
-        'conditions': [
-          ['component=="static_library"', {
-            'defines': [
-              'U_STATIC_IMPLEMENTATION',
-            ],
-          }],
-        ],
-        'include_dirs': [
-          'source/common',
-          'source/i18n',
-        ],
-        'msvs_disabled_warnings': [4005, 4068, 4355, 4996, 4267],
-      },
+    ['use_system_icu==0 or want_separate_host_toolset==1', {
       'targets': [
         {
           'target_name': 'icudata',
           'type': 'static_library',
           'defines': [
             'U_HIDE_DATA_SYMBOL',
           ],
           'sources': [
              # These are hand-generated, but will do for now.  The linux
              # version is an identical copy of the (mac) icudt46l_dat.S file,
              # modulo removal of the .private_extern and .const directives and
              # with no leading underscore on the icudt46_dat symbol.
              'android/icudt46l_dat.S',
              'linux/icudt46l_dat.S',
              'mac/icudt46l_dat.S',
           ],
           'conditions': [
+            [ 'use_system_icu==1', {
+              'toolsets': ['host'],
+            }, {
+              'toolsets': ['host', 'target'],
+            }],
             [ 'OS == "win"', {
               'type': 'none',
               'copies': [
                 {
                   'destination': '<(PRODUCT_DIR)',
                   'files': [
                     'windows/icudt.dll',
                   ],
                 },
               ],
@@ skipping 190 matching lines @@
           ],
           'dependencies': [
             'icuuc',
           ],
           'direct_dependent_settings': {
             'include_dirs': [
               'source/i18n',
             ],
           },
           'conditions': [
+            [ 'use_system_icu==1', {
+              'toolsets': ['host'],
+            }, {
+              'toolsets': ['host', 'target'],
+            }],
             [ 'os_posix == 1 and OS != "mac" and OS != "ios"', {
               # Since ICU wants to internally use its own deprecated APIs, don't
               # complain about it.
               'cflags': [
                 '-Wno-deprecated-declarations',
               ],
               'cflags_cc': [
                 '-frtti',
               ],
             }],
@@ skipping 226 matching lines @@
             ],
             'conditions': [
               [ 'component=="static_library"', {
                 'defines': [
                   'U_STATIC_IMPLEMENTATION',
                 ],
               }],
             ],
           },
           'conditions': [
+            [ 'use_system_icu==1', {
+              'toolsets': ['host'],
+            }, {
+              'toolsets': ['host', 'target'],
+            }],
             [ 'OS == "win"', {
               'sources': [
                 'source/stubdata/stubdata.c',
               ],
             }],
             [ 'os_posix == 1 and OS != "mac" and OS != "ios"', {
               'cflags': [
                 # Since ICU wants to internally use its own deprecated APIs,
                 # don't complain about it.
                 '-Wno-deprecated-declarations',
@@ skipping 47 matching lines @@
               'cflags': [
                 '-Wno-deprecated-declarations',
                 '-Wno-logical-op-parentheses',
                 '-Wno-tautological-compare',
                 '-Wno-switch',
               ],
             }],
           ],
         },
       ],
-    }, { # use_system_icu != 0
+    }],
+    ['use_system_icu==1', {
       'targets': [
         {
           'target_name': 'system_icu',
           'type': 'none',
           'conditions': [
+            ['want_separate_host_toolset==1', {
+              'toolsets': ['target'],
+            }, {
+              'toolsets': ['host', 'target'],
+            }],
             ['OS=="android"', {
               'direct_dependent_settings': {
                 'include_dirs': [
                   '<(android_src)/external/icu4c/common',
                   '<(android_src)/external/icu4c/i18n',
                 ],
               },
               'link_settings': {
                 'libraries': [
                   '-licui18n',
@@ skipping 10 matching lines @@
                 ],
               },
             }],
           ],
         },
         {
           'target_name': 'icudata',
           'type': 'none',
           'dependencies': ['system_icu'],
           'export_dependent_settings': ['system_icu'],
+          'conditions': [
+            ['want_separate_host_toolset==1', {
+              'toolsets': ['target'],
+            }, {
+              'toolsets': ['host', 'target'],
+            }],
+          ],
         },
         {
           'target_name': 'icui18n',
           'type': 'none',
           'dependencies': ['system_icu'],
           'export_dependent_settings': ['system_icu'],
           'variables': {
             'headers_root_path': 'source/i18n',
             'header_filenames': [
               # This list can easily be updated using the command below:
@@ skipping 66 matching lines @@
               'unicode/usearch.h',
               'unicode/uspoof.h',
               'unicode/utmscale.h',
               'unicode/utrans.h',
               'unicode/vtzone.h',
             ],
           },
           'includes': [
             '../../build/shim_headers.gypi',
           ],
+          'conditions': [
+            ['want_separate_host_toolset==1', {
+              'toolsets': ['target'],
+            }, {
+              'toolsets': ['host', 'target'],
+            }],
+          ],
         },
         {
           'target_name': 'icuuc',
           'type': 'none',
           'dependencies': ['system_icu'],
           'export_dependent_settings': ['system_icu'],
           'variables': {
             'headers_root_path': 'source/common',
             'header_filenames': [
               # This list can easily be updated using the command below:
@@ skipping 84 matching lines @@
               'unicode/utrace.h',
               'unicode/utypeinfo.h',
               'unicode/utypes.h',
               'unicode/uvernum.h',
               'unicode/uversion.h',
             ],
           },
           'includes': [
             '../../build/shim_headers.gypi',
           ],
+          'conditions': [
+            ['want_separate_host_toolset==1', {
+              'toolsets': ['target'],
+            }, {
+              'toolsets': ['host', 'target'],
+            }],
+          ],
         },
       ],
     }],
   ],
 }