ART: Place conditionally needed include in #ifdef

Mingw's wchar.h has some broken macros that are bypassed when stdio
is included. However, in general the stdio include is superfluous
and a huge transitive dependency.

Test: mmma art
Change-Id: I07c95e2085f5b70a60fee0c2cafa72b30aca4d15
diff --git a/libartbase/base/time_utils.h b/libartbase/base/time_utils.h
index 15805f3..69c867c 100644
--- a/libartbase/base/time_utils.h
+++ b/libartbase/base/time_utils.h
@@ -17,14 +17,15 @@
 #ifndef ART_LIBARTBASE_BASE_TIME_UTILS_H_
 #define ART_LIBARTBASE_BASE_TIME_UTILS_H_
 
-#include <stdint.h>
-#include <stdio.h>  // Needed for correct _WIN32 build.
+#ifdef _WIN32
+#include <stdio.h>  // Needed for correct macro definitions.
+#endif
+
 #include <time.h>
 
+#include <cstdint>
 #include <string>
 
-#include "macros.h"
-
 namespace art {
 
 enum TimeUnit {