Fix libnativeloader unit tests being skipped.

ART_TARGET_ANDROID was only defined in art_defaults, which wasn't
imported into libnativeloader_test. However doing that imports a lot of
stuff, including compiler pickiness that doesn't work with cxxabi.h
included via gtest.h. We instead make ART_TARGET_(ANDROID|LINUX)
implicitly defined in all art_cc_* module types.

These tests have probably not run since https://r.android.com/1295365.
Also fixed the accumulated bitrot.

Test: atest libnativeloader_test, check that 25 tests pass.
Test: Plant a test failure in native_loader_test.cpp, check that
  presubmit fails.
Bug: 154074847
Bug: 137356719
Change-Id: I4e9d4dc8d78c91a7b750b8de0ab7db2114b154ac
4 files changed