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
diff --git a/tests/stdio_test.cpp b/tests/stdio_test.cpp
index 4725350..655ad3f 100644
--- a/tests/stdio_test.cpp
+++ b/tests/stdio_test.cpp
@@ -219,7 +219,7 @@
 }
 
 TEST(stdio, snprintf_n) {
-#if !defined(__GLIBC__)
+#if defined(__BIONIC__)
   // http://b/14492135
   char buf[32];
   int i = 1234;
@@ -460,7 +460,7 @@
 
   errno = 0;
   EXPECT_EQ(EOF, fwprintf(fp, L"hello"));
-#if !defined(__GLIBC__)
+#if defined(__BIONIC__)
   EXPECT_EQ(EBADF, errno);
 #endif
 
@@ -478,7 +478,7 @@
 
   errno = 0;
   EXPECT_EQ(WEOF, fputwc(L'x', fp));
-#if !defined(__GLIBC__)
+#if defined(__BIONIC__)
   EXPECT_EQ(EBADF, errno);
 #endif
 }
@@ -521,7 +521,7 @@
   ASSERT_EQ(mb_four_bytes, static_cast<wchar_t>(fgetwc(fp)));
   EXPECT_EQ(0, fgetpos(fp, &pos5));
 
-#ifdef __BIONIC__
+#if defined(__BIONIC__)
   // Bionic's fpos_t is just an alias for off_t. This is inherited from OpenBSD
   // upstream. Glibc differs by storing the mbstate_t inside its fpos_t. In
   // Bionic (and upstream OpenBSD) the mbstate_t is stored inside the FILE
@@ -586,9 +586,9 @@
   // Store the "inside multi byte" position.
   fpos_t pos_inside_mb;
   ASSERT_EQ(0, fgetpos(fp, &pos_inside_mb));
-  #ifdef __BIONIC__
-    ASSERT_EQ(offset_inside_mb, static_cast<off_t>(pos_inside_mb));
-  #endif
+#if defined(__BIONIC__)
+  ASSERT_EQ(offset_inside_mb, static_cast<off_t>(pos_inside_mb));
+#endif
 
   // Reading from within a byte should produce an error.
   ASSERT_EQ(WEOF, fgetwc(fp));