Install python module into gdb auto-load directory.

--- a/Makefile.in
+++ b/Makefile.in
@@ -2189,9 +2189,9 @@ install-data-local: $(srcdir)/isl.py
 	case $$libisl in \
 	'') echo Cannot find isl library name. GDB bindings not installed.;; \
 	*) echo $(INSTALL_DATA) $(srcdir)/isl.py \
-		$(DESTDIR)$(libdir)/$$libisl-gdb.py; \
-	test -z "$(libdir)" || $(MKDIR_P) "$(DESTDIR)$(libdir)"; \
-	$(INSTALL_DATA) $(srcdir)/isl.py $(DESTDIR)$(libdir)/$$libisl-gdb.py; esac
+		$(DESTDIR)$(prefix)/share/gdb/auto-load$(libdir)/$$libisl-gdb.py; \
+	test -z "$(libdir)" || $(MKDIR_P) "$(DESTDIR)$(prefix)/share/gdb/auto-load$(libdir)"; \
+	$(INSTALL_DATA) $(srcdir)/isl.py $(DESTDIR)$(prefix)/share/gdb/auto-load$(libdir)/$$libisl-gdb.py; esac
 
 # Tell versions [3.59,3.63) of GNU make to not export all variables.
 # Otherwise a system limit (for SysV at least) may be exceeded.