patch posixmodule umask to accept 0 as a mock setting

- this is needed by pip and venv

Author: cosminbasca

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/PosixModuleBuiltins.java

@@ -1633,6 +1633,10 @@ abstract static class UmaskNode extends PythonBuiltinNode {
         int getAndSetUmask(int umask) {
             if (umask == 0022) {
                 return 0022;
+            } if (umask == 0) {
+                // TODO: change me, this does not really set the umask, workaround needed for pip
+                // it returns the previous mask (which in our case is always 0022)
+                return 0022;
             } else {
                 throw raise(NotImplementedError, "setting the umask to anything other than the default");
             }