Consistently use #if defined(__BIONIC__) in tests.

I've also switched some tests to be positive rather than negative,
because !defined is slightly harder to reason about and there are
only two cases: bionic and glibc.

Change-Id: I8d3ac40420ca5aead3e88c69cf293f267273c8ef

tests/locale_test.cpp

@@ -58,7 +58,7 @@ TEST(locale, setlocale) {
   EXPECT_EQ(NULL, setlocale(13, NULL));
   EXPECT_EQ(EINVAL, errno);
 
-#if __BIONIC__
+#if defined(__BIONIC__)
   // The "" locale is implementation-defined. For bionic, it's the C locale.
   // glibc will give us something like "en_US.UTF-8", depending on the user's configuration.
   EXPECT_STREQ("C", setlocale(LC_ALL, ""));