Fourth attempt at the following. Unreviewed, this was originally reviewed in http://codereview.c...

base/base.gypi

 # Copyright (c) 2011 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.
 
 {
   'target_defaults': {
     'variables': {
       'base_target': 0,
     },
     'target_conditions': [
@@ skipping 440 matching lines @@
             ],
           }],
         ],
       }],
     ],
   },
   'targets': [
     {
       'target_name': 'base',
       'type': '<(component)',
+      'toolsets': ['host', 'target'],
       'variables': {
         'base_target': 1,
       },
       'dependencies': [
         'base_static',
         '../third_party/modp_b64/modp_b64.gyp:modp_b64',
         'third_party/dynamic_annotations/dynamic_annotations.gyp:dynamic_annotations',
       ],
       # TODO(gregoryd): direct_dependent_settings should be shared with the
       #  64-bit target, but it doesn't work due to a bug in gyp
@@ skipping 194 matching lines @@
             },
           },
         },
       ],
     }],
     [ 'os_posix==1 and OS!="mac"', {
       'targets': [
         {
           'target_name': 'symbolize',
           'type': 'static_library',
+          'toolsets': ['host', 'target'],
           'variables': {
             'chromium_code': 0,
           },
           'conditions': [
             [ 'OS == "solaris"', {
               'include_dirs': [
                 '/usr/gnu/include',
                 '/usr/gnu/include/libelf',
               ],
             },],
           ],
           'cflags': [
             '-Wno-sign-compare',
           ],
           'cflags!': [
             '-Wextra',
           ],
           'sources': [
             'third_party/symbolize/symbolize.cc',
             'third_party/symbolize/demangle.cc',
           ],
         },
         {
           'target_name': 'xdg_mime',
           'type': 'static_library',
+          'toolsets': ['host', 'target'],
           'variables': {
             'chromium_code': 0,
           },
           'cflags!': [
             '-Wextra',
           ],
           'sources': [
             'third_party/xdg_mime/xdgmime.c',
             'third_party/xdg_mime/xdgmime.h',
             'third_party/xdg_mime/xdgmimealias.c',
             'third_party/xdg_mime/xdgmimealias.h',
             'third_party/xdg_mime/xdgmimecache.c',
             'third_party/xdg_mime/xdgmimecache.h',
             'third_party/xdg_mime/xdgmimeglob.c',
             'third_party/xdg_mime/xdgmimeglob.h',
             'third_party/xdg_mime/xdgmimeicon.c',
             'third_party/xdg_mime/xdgmimeicon.h',
             'third_party/xdg_mime/xdgmimeint.c',
             'third_party/xdg_mime/xdgmimeint.h',
             'third_party/xdg_mime/xdgmimemagic.c',
             'third_party/xdg_mime/xdgmimemagic.h',
             'third_party/xdg_mime/xdgmimeparent.c',
             'third_party/xdg_mime/xdgmimeparent.h',
           ],
         },
       ],
     }],
   ],
 }