0022972: Eliminate macro definitions that has compiler-provided analogs (WNT and so on)

1) Macro definition WNT replaced by _WIN32 and _MSC_VER for platform and compiler detection accordingly.
2) Macro definition LIN replaced by __linux__ macro.
3) Macro definition DEB replaced by OCCT_DEBUG macro.

src/Message/Message_MsgFile.cxx

@@ -63,7 +63,7 @@ Standard_Boolean Message_MsgFile::Load (const Standard_CString theDirName,
   {
     TCollection_AsciiString aFileName = aDirList.Token (" \t\n", i);
     if (aFileName.IsEmpty()) break;
-#ifdef WNT
+#ifdef _WIN32
     aFileName += '\\';
 #else
     aFileName += '/';