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/BRepMesh/BRepMesh_Delaun.cxx

@@ -2350,7 +2350,7 @@ Standard_Real BRepMesh_Delaun::polyArea(const BRepMesh::SequenceOfInteger& thePo
   return aArea / 2.;
 }
 
-#ifdef DEB
+#ifdef OCCT_DEBUG
 //=======================================================================
 //function : BRepMesh_DumpPoly
 //purpose  : 

src/BRepMesh/BRepMesh_DiscretFactory.cxx

@@ -31,11 +31,11 @@ namespace
                                  TCollection_AsciiString& theLibName)
   {
     theLibName = "";
-  #ifndef WNT
+  #ifndef _WIN32
     theLibName += "lib";
   #endif
     theLibName += theDefaultName;
-  #ifdef WNT
+  #ifdef _WIN32
     theLibName += ".dll";
   #elif __APPLE__
     theLibName += ".dylib";