The former is from googletest.test.mk, whereas the latter is from plain.test.mk.
As noted in r344328, Kyua will adopt more native GoogleTest support. Thus, it's
more desirable to make the test interface more of an opaque blackbox for the
testcase implementer.
- Look up the corresponding non-*_main libraries via LDFLAGS using the
directories provided in src.libnames.mk. This will allow the libraries to
be built in the "make libraries" phase of buildworld.
- gtest_main relies on gtest, but didn't explicitly call out the dependency
in `LIBADD`. Fill in this missing blank.
