Add GN target for the sample shell

gypfiles/toolchain.gypi

 # Copyright 2013 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
@@ skipping 63 matching lines @@
 
     # Chrome needs this definition unconditionally. For standalone V8 builds,
     # it's handled in gypfiles/standalone.gypi.
     'want_separate_host_toolset%': 1,
 
     # Toolset the d8 binary should be compiled for. Possible values are 'host'
     # and 'target'. If you want to run v8 tests, it needs to be set to 'target'.
     # The setting is ignored if want_separate_host_toolset is 0.
     'v8_toolset_for_d8%': 'target',
 
+    # Toolset the shell binary should be compiled for. Possible values are
+    # 'host' and 'target'.
+    # The setting is ignored if want_separate_host_toolset is 0.
+    'v8_toolset_for_shell%': 'target',
+
     'host_os%': '<(OS)',
     'werror%': '-Werror',
     # For a shared library build, results in "libv8-<(soname_version).so".
     'soname_version%': '',
 
     # Allow to suppress the array bounds warning (default is no suppression).
     'wno_array_bounds%': '',
 
     # Override where to find binutils
     'binutils_dir%': '',
@@ skipping 1291 matching lines @@
             ],
           },
           'Release_x64': {
             'inherit_from': ['ReleaseBase'],
           },
         }],
       ],
     },  # configurations
   },  # target_defaults
 }