Fix usage of snprintf for MSVC

Older versions of MSVC don't have a snprintf functions. Some files
were already working around that, but not all of them. Instead of
copying the logic into every file, I centralize it into a new
stdio.h wrapper file and make other files include that.

BUG=
R=mark@chromium.org

Review URL: https://codereview.chromium.org/1602563003 .

Patch from Pavel Labath <labath@google.com>.

src/processor/stackwalk_common.cc

@@ -35,13 +35,13 @@
 #include "processor/stackwalk_common.h"
 
 #include <assert.h>
-#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include <string>
 #include <vector>
 
+#include "common/stdio.h"
 #include "common/using_std_string.h"
 #include "google_breakpad/processor/call_stack.h"
 #include "google_breakpad/processor/code_module.h"