The patch no longer applies to trunk, but that would be trivial to fix.

Changes like these have been accepted with little resistance in the past 
(see e.g. issue651362), so I don't see why this patch has been pending 
for  so long.  (In general, I am -0 on adding const modifiers because 
they tend to trigger an avalanche of changes, but arguably this is the 
"right thing to do.")   

A few comments:

* Documentation needs to be updated in Doc/c-api/sys.rst. 

* Any reason why PySys_SetPath(char *) is left out?

* Same for PySys_SetArgv(int, char **)

* Similar changes are proposed in issue1772673.  Maybe these two issues 
can be dealt with together.