Get libbase tests working on Windows.

Tests using files from /proc still fail on Windows (obviously), but
all tests are passing when run in Wine.

Change-Id: Ie4c3ba65b642202f8fcaec73332a53bee6115fba
diff --git a/base/stringprintf_test.cpp b/base/stringprintf_test.cpp
index 5cc2086..54b2b6c 100644
--- a/base/stringprintf_test.cpp
+++ b/base/stringprintf_test.cpp
@@ -20,11 +20,14 @@
 
 #include <string>
 
+// The z size sepcifier isn't supported on Windows, so this test isn't useful.
+#if !defined(_WIN32)
 TEST(StringPrintfTest, HexSizeT) {
   size_t size = 0x00107e59;
   EXPECT_EQ("00107e59", android::base::StringPrintf("%08zx", size));
   EXPECT_EQ("0x00107e59", android::base::StringPrintf("0x%08zx", size));
 }
+#endif
 
 TEST(StringPrintfTest, StringAppendF) {
   std::string s("a");