[snapshot] Move builtins generation into mksnapshot

test/cctest/cctest.status

Index: test/cctest/cctest.status
diff --git a/test/cctest/cctest.status b/test/cctest/cctest.status
index 6bf2354b1d49d20300133e836cc5c071f073fc8c..60cc1a444c13206594fcb9d612c546b32dd9269c 100644
--- a/test/cctest/cctest.status
+++ b/test/cctest/cctest.status
@@ -197,6 +197,10 @@
   'test-api/ExternalWrap': [PASS, SLOW],
   'test-api/FastReturnValues*': [PASS, SLOW],
   'test-decls/CrossScriptReferences_Simple2': [PASS, SLOW],
+  # "WithWarmup" means starting from a snapshot, for which nosnap builds lack
+  # support.
+  'test-serialize/CustomSnapshotDataBlobWithWarmup': [SKIP],
+  'test-serialize/SnapshotDataBlobWithWarmup': [SKIP],
 }],  # 'no_snap == True'
 ['no_snap == False', {
   # FunctionEntryHooks require bootstrapping from scratch.