Also build parsing/test-scanner-streams.

crrev.com/2339933002 and crrev.com/2314663002 were overlapping, so
this slipped through the cracks.

R=jochen@chromium.org
BUG=v8:4947, chromium:646794

Review-Url: https://codereview.chromium.org/2343093002
Cr-Commit-Position: refs/heads/master@{#39474}

test/cctest/BUILD.gn

@@ -81,6 +81,7 @@ v8_executable("cctest") {
     "interpreter/test-source-positions.cc",
     "libplatform/test-tracing.cc",
     "libsampler/test-sampler.cc",
+    "parsing/test-scanner-streams.cc",
     "print-extension.cc",
     "profiler-extension.cc",
     "test-access-checks.cc",