bionic tests: use GTEST_SKIP.

Also be a bit more to the point in our messages, focusing on "why" not
"what".

Test: ran tests
Change-Id: I297806c7a102bd52602dcd2fcf7a2cd34aba3a11
diff --git a/tests/link_test.cpp b/tests/link_test.cpp
index 1bdee9f..cf5fc0b 100644
--- a/tests/link_test.cpp
+++ b/tests/link_test.cpp
@@ -231,6 +231,6 @@
   }
   ASSERT_TRUE(found);
 #else
-  GTEST_LOG_(INFO) << "dl_unwind_find_exidx is an ARM-only API\n";
+  GTEST_SKIP() << "dl_unwind_find_exidx is an ARM-only API";
 #endif
 }