It is not specified whether the python sitedir is located within the native
ABI's $libdir folder. This breaks Gentoo's py3.7 and 3.8 installations.

--- a/Makefile.in
+++ b/Makefile.in
@@ -154,9 +154,9 @@
 	ln -sf $(LIBNEWTSH) $(DESTDIR)/$(libdir)/$(LIBNEWTSONAME)
 	[ -n "$(WHIPTCLSO)" ] && install -m 755 whiptcl.$(SOEXT) $(DESTDIR)/$(libdir) || :
 	[ -n "$(PYTHONVERS)" ] && for ver in $(PYTHONVERS) ; do \
-	   [ -d $(DESTDIR)/$(libdir)/$$ver/site-packages ] || install -m 755 -d $(DESTDIR)/$(libdir)/$$ver/site-packages ;\
-	   install -m 755 $$ver/_snack.$(SOEXT) $(DESTDIR)/$(libdir)/$$ver/site-packages ;\
-	   install -m 644 snack.py $(DESTDIR)/$(libdir)/$$ver/site-packages ;\
+	   [ -d $(DESTDIR)/$(PYTHON_SITEDIR) ] || install -m 755 -d $(DESTDIR)/$(PYTHON_SITEDIR) ;\
+	   install -m 755 $$ver/_snack.$(SOEXT) $(DESTDIR)/$(PYTHON_SITEDIR) ;\
+	   install -m 644 snack.py $(DESTDIR)/$(PYTHON_SITEDIR) ;\
 	done || :
 
 Makefile: configure.ac