0029151: GCC 7.1 warnings "this statement may fall through" [-Wimplicit-fallthrough=]

New macro Standard_FALLTHROUGH is defined for use in a switch statement immediately before a case label, if code associated with the previous case label may fall through to that
next label (i.e. does not end with "break" or "return" etc.).
This macro indicates that the fall through is intentional and should not be diagnosed by a compiler that warns on fallthrough.

The macro is inserted in places that currently generate such warning message and where fallthrough is intentional.

Doxygen comments are provided for this and other macros in Standard_Macro.hxx.

src/IntPatch/IntPatch_ALineToWLine.cxx

@@ -101,6 +101,7 @@ static IntPatch_SpecPntType IsPoleOrSeam(const Handle(Adaptor3d_HSurface)& theS1
           break;
         }
       }
+      Standard_FALLTHROUGH
     case GeomAbs_Torus:
       if(aType == GeomAbs_Torus)
       {
@@ -113,6 +114,7 @@ static IntPatch_SpecPntType IsPoleOrSeam(const Handle(Adaptor3d_HSurface)& theS1
           break;
         }
       }
+      Standard_FALLTHROUGH
     case GeomAbs_Cylinder:
       theSingularSurfaceID = i + 1;
       AddVertexPoint(theLine, theVertex, theArrPeriods);

src/IntPatch/IntPatch_ImpPrmIntersection.cxx

@@ -428,6 +428,7 @@ void Recadre(const Standard_Boolean ,
   case GeomAbs_Torus:
     while(V1<(V1p-1.5*M_PI)) V1+=M_PI+M_PI;
     while(V1>(V1p+1.5*M_PI)) V1-=M_PI+M_PI;
+    Standard_FALLTHROUGH
   case GeomAbs_Cylinder:
   case GeomAbs_Cone:
   case GeomAbs_Sphere:
@@ -441,6 +442,7 @@ void Recadre(const Standard_Boolean ,
   case GeomAbs_Torus:
     while(V2<(V2p-1.5*M_PI)) V2+=M_PI+M_PI;
     while(V2>(V2p+1.5*M_PI)) V2-=M_PI+M_PI;
+    Standard_FALLTHROUGH
   case GeomAbs_Cylinder:
   case GeomAbs_Cone:
   case GeomAbs_Sphere:

src/IntPatch/IntPatch_Intersection.cxx

@@ -166,6 +166,7 @@ void IntPatch_Intersection::Perform(const Handle(Adaptor3d_HSurface)&  S1,
       if (Intersector.IsDone() && Intersector.IsEmpty())
         break;
     }
+    Standard_FALLTHROUGH
   default:
     {
       IntPatch_PrmPrmIntersection interpp;