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/Poly/Poly_CoherentNode.cxx

@@ -16,7 +16,7 @@
 #include <Poly_CoherentNode.hxx>
 #include <Poly_CoherentTriangle.hxx>
 
-#ifdef WNT
+#ifdef _MSC_VER
 #pragma warning(disable:4996)
 #endif
 

src/Poly/Poly_CoherentTriPtr.hxx

@@ -21,7 +21,7 @@
 
 class Poly_CoherentTriangle;
 
-#ifdef WNT
+#ifdef _MSC_VER
 #pragma warning (push)
 #pragma warning(disable:4355) //'this' : used in base member initializer list
 #endif
@@ -177,7 +177,7 @@ class Poly_CoherentTriPtr
   friend class Iterator;
 };
 
-#ifdef WNT
+#ifdef _MSC_VER
 #pragma warning (pop)
 #endif