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/minidump.cc

@@ -38,15 +38,11 @@
 #include <assert.h>
 #include <fcntl.h>
 #include <stddef.h>
-#include <stdio.h>
 #include <string.h>
 #include <time.h>
 
 #ifdef _WIN32
 #include <io.h>
-#if defined(_MSC_VER) && _MSC_VER < 1900
-#define snprintf _snprintf
-#endif
 #else  // _WIN32
 #include <unistd.h>
 #endif  // _WIN32
@@ -60,6 +56,7 @@
 #include "processor/range_map-inl.h"
 
 #include "common/scoped_ptr.h"
+#include "common/stdio.h"
 #include "google_breakpad/processor/dump_context.h"
 #include "processor/basic_code_module.h"
 #include "processor/basic_code_modules.h"