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/libgen_test.cpp b/tests/libgen_test.cpp
index d5b5eb6..24f7923 100644
--- a/tests/libgen_test.cpp
+++ b/tests/libgen_test.cpp
@@ -78,7 +78,7 @@
   TestBasename(".", ".", 1, buf, sizeof(buf), 0);
   TestBasename("..", "..", 2, buf, sizeof(buf), 0);
 #else // __BIONIC__
-  GTEST_LOG_(INFO) << "This test does nothing.\n";
+  GTEST_SKIP() << "basename_r is only available on 32-bit bionic";
 #endif // __BIONIC__
 }
 
@@ -95,6 +95,6 @@
   TestDirname(".", ".", 1, buf, sizeof(buf), 0);
   TestDirname("..", ".", 1, buf, sizeof(buf), 0);
 #else // __BIONIC__
-  GTEST_LOG_(INFO) << "This test does nothing.\n";
+  GTEST_SKIP() << "dirname_r is only available on 32-bit bionic";
 #endif // __BIONIC__
 }