Build "snapshot_blob.bin" only for the host when using separate toolsets.

tools/gyp/v8.gyp

Index: tools/gyp/v8.gyp
diff --git a/tools/gyp/v8.gyp b/tools/gyp/v8.gyp
index 708c091cf88dd3083fd38ec727af1b705b7dc143..be9fb3ee8d2f0175b269feefe5215e9931034972 100644
--- a/tools/gyp/v8.gyp
+++ b/tools/gyp/v8.gyp
@@ -55,9 +55,12 @@
           # to appear before libv8_snapshot.a so it's listed explicitly.
           'dependencies': ['v8_base', 'v8_nosnapshot'],
         }],
-        ['v8_use_external_startup_data==1', {
+        ['v8_use_external_startup_data==1 and want_separate_host_toolset==0', {
           'dependencies': ['v8_base', 'v8_external_snapshot'],
         }],
+        ['v8_use_external_startup_data==1 and want_separate_host_toolset==1', {
+          'dependencies': ['v8_base', 'v8_external_snapshot#host'],
+        }],
         ['component=="shared_library"', {
           'type': '<(component)',
           'sources': [
@@ -219,7 +222,7 @@
       'type': 'static_library',
       'conditions': [
         ['want_separate_host_toolset==1', {
-          'toolsets': ['host', 'target'],
+          'toolsets': ['host'],
           'dependencies': [
             'mksnapshot#host',
             'js2c#host',