IE: Fix Windows compilation on MSVC (adapt PR: #7206 from master branch) (#7486)

`Win32` may be undefined when MSVC is used, see:
https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros?redirectedfrom=MSDN&view=msvc-160

Signed-off-by: Karol Trzcinski <karolx.trzcinski@intel.com>

inference-engine/src/inference_engine/compilation_context.cpp

@@ -7,7 +7,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 
-#ifndef WIN32
+#ifndef _WIN32
 #include <unistd.h>
 #endif
 #include <xml_parse_utils.h>
@@ -24,7 +24,7 @@
 #include "transformations/rt_info/primitives_priority_attribute.hpp"
 #include "file_utils.h"
 
-#ifdef WIN32
+#ifdef _WIN32
 #define stat _stat
 #endif