Fix clang build breakage (-Werror -Wformat).

Use %zd for size_t. Note that this will break only on (-plus-)aosp because
clang is disabled on the N development branches.

bug: 30963384
Change-Id: I4b5ba7caf15bc2ebf5bb3395d82170ec786ed50c
diff --git a/core/jni/fd_utils-inl.h b/core/jni/fd_utils-inl.h
index bd68625..1f34b02 100644
--- a/core/jni/fd_utils-inl.h
+++ b/core/jni/fd_utils-inl.h
@@ -404,7 +404,7 @@
       //
       // TODO(narayan): This will be an error in a future android release.
       // error = true;
-      ALOGW("Zygote opened %d new file descriptor(s).", open_fds.size());
+      ALOGW("Zygote opened %zd new file descriptor(s).", open_fds.size());
 
       // TODO(narayan): This code will be removed in a future android release.
       std::set<int>::const_iterator it;