CMake: Use GCC7's -Wimplicit-fallthrough=5

Use to avoid accidental missing break statements,
use ATTR_FALLTHROUGH to suppress.

source/blender/python/intern/bpy_rna.c

@@ -806,7 +806,7 @@ static PyObject *pyrna_struct_richcmp(PyObject *a, PyObject *b, int op)
 	switch (op) {
 		case Py_NE:
 			ok = !ok;
-			/* fall-through */
+			ATTR_FALLTHROUGH;
 		case Py_EQ:
 			res = ok ? Py_False : Py_True;
 			break;
@@ -836,7 +836,7 @@ static PyObject *pyrna_prop_richcmp(PyObject *a, PyObject *b, int op)
 	switch (op) {
 		case Py_NE:
 			ok = !ok;
-			/* fall-through */
+			ATTR_FALLTHROUGH;
 		case Py_EQ:
 			res = ok ? Py_False : Py_True;
 			break;
@@ -5168,7 +5168,7 @@ static PyObject *pyrna_param_to_py(PointerRNA *ptr, PropertyRNA *prop, void *dat
 							ret = Matrix_CreatePyObject(data, 3, 3, NULL);
 							break;
 						}
-						/* fall-through */
+						ATTR_FALLTHROUGH;
 #endif
 					default:
 						ret = PyTuple_New(len);

source/blender/python/mathutils/mathutils_Color.c

@@ -173,7 +173,7 @@ static PyObject *Color_richcmpr(PyObject *a, PyObject *b, int op)
 	switch (op) {
 		case Py_NE:
 			ok = !ok;
-			/* fall-through */
+			ATTR_FALLTHROUGH;
 		case Py_EQ:
 			res = ok ? Py_False : Py_True;
 			break;

source/blender/python/mathutils/mathutils_Euler.c

@@ -65,7 +65,7 @@ static PyObject *Euler_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 		case 2:
 			if ((order = euler_order_from_string(order_str, "mathutils.Euler()")) == -1)
 				return NULL;
-			/* fall-through */
+			ATTR_FALLTHROUGH;
 		case 1:
 			if (mathutils_array_parse(eul, EULER_SIZE, EULER_SIZE, seq, "mathutils.Euler()") == -1)
 				return NULL;
@@ -370,7 +370,7 @@ static PyObject *Euler_richcmpr(PyObject *a, PyObject *b, int op)
 	switch (op) {
 		case Py_NE:
 			ok = !ok;
-			/* fall-through */
+			ATTR_FALLTHROUGH;
 		case Py_EQ:
 			res = ok ? Py_False : Py_True;
 			break;

source/blender/python/mathutils/mathutils_Matrix.c

@@ -2034,7 +2034,7 @@ static PyObject *Matrix_richcmpr(PyObject *a, PyObject *b, int op)
 	switch (op) {
 		case Py_NE:
 			ok = !ok;
-			/* fall-through */
+			ATTR_FALLTHROUGH;
 		case Py_EQ:
 			res = ok ? Py_False : Py_True;
 			break;

source/blender/python/mathutils/mathutils_Quaternion.c

@@ -552,7 +552,7 @@ static PyObject *Quaternion_richcmpr(PyObject *a, PyObject *b, int op)
 	switch (op) {
 		case Py_NE:
 			ok = !ok;
-			/* fall-through */
+			ATTR_FALLTHROUGH;
 		case Py_EQ:
 			res = ok ? Py_False : Py_True;
 			break;