tools_common.h: (msvs) avoid redefining off_t

in some configurations MSVS will define _off_t / off_t in wchar.h; the
former is used locally while the latter is for compatibility. this
change overrides off_t as in the past and sets _OFF_T_DEFINED to prevent
a clash in types.

Change-Id: I9b0e6db586a0a2729b545d93edfc56570d2fcf97

tools_common.h

@@ -22,10 +22,12 @@
 #endif
 
 #if defined(_MSC_VER)
-/* MSVS doesn't define off_t, and uses _f{seek,tell}i64. */
-typedef __int64 off_t;
+/* MSVS uses _f{seek,tell}i64. */
 #define fseeko _fseeki64
 #define ftello _ftelli64
+typedef long _off_t;  // NOLINT - MSVS compatible type
+typedef __int64 off_t;  // fseeki64 compatible type
+#define _OFF_T_DEFINED
 #elif defined(_WIN32)
 /* MinGW defines off_t as long and uses f{seek,tell}o64/off64_t for large
  * files. */