test: Link gtest_main in test binaries

The library gtest_main provides a 'main' function which runs the tests
and reports whether they passed or failed. When it's not included,
linking fails because there is no 'main' function.

Signed-off-by: Benjamin Fair <benjaminfair@google.com>
Change-Id: I79310447053e07eb1873fc353ef99b0b12223328
1 file changed