Add <cstdio> include to string_builder.cc to support Android NDK r17

<cstdio> is needed for std::vsnprintf() on Android NDK r17

Bug: NONE
Change-Id: Ib533bc64fcc41deb68613f494b6777dcf805907e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/137001
Commit-Queue: Tommi <tommi@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27956}
diff --git a/rtc_base/strings/string_builder.cc b/rtc_base/strings/string_builder.cc
index adf4fa9..73d763a 100644
--- a/rtc_base/strings/string_builder.cc
+++ b/rtc_base/strings/string_builder.cc
@@ -11,6 +11,7 @@
 #include "rtc_base/strings/string_builder.h"
 
 #include <stdarg.h>
+#include <cstdio>
 #include <cstring>
 
 #include "rtc_base/checks.h"