Enable build with shared libraries.

This adaptation will allow build v8 when the component is defined as
shared library. Without this, at linking phase of the unittests will be
displayed error messages for undefined references.

TEST=
BUG=

Review-Url: https://codereview.chromium.org/2853483002
Cr-Commit-Position: refs/heads/master@{#45126}

test/unittests/unittests.gyp

@@ -193,6 +193,7 @@
         '../../src/v8.gyp:v8',
         '../../src/v8.gyp:v8_libbase',
         '../../src/v8.gyp:v8_libplatform',
+        '../../src/v8.gyp:v8_maybe_snapshot',
       ],
       'include_dirs': [
         '../..',