ARROW-1375: [C++] Remove dependency on msvc version for Snappy build

Author: Max Risuhin <risuhin.max@gmail.com>

Closes #980 from MaxRis/ARROW-1375 and squashes the following commits:

f5e4156 [Max Risuhin] ARROW-1375: [C++] Remove dependency on msvc version for Snappy build

Author: maxhora

cpp/cmake_modules/SnappyConfig.h

@@ -29,7 +29,7 @@
 #ifndef SNAPPY_CONFIG_H
 #define SNAPPY_CONFIG_H 1
 
-#if defined(_MSC_VER) && (_MSC_VER <= 1910)
+#if defined(_MSC_VER)
 typedef __int64 ssize_t;
 #endif