pull Rules.mak from top_srcdir as pointed out by Robert P. J. Day on the mailing list
diff --git a/editors/Makefile b/editors/Makefile
index 941c4c7..2279009 100644
--- a/editors/Makefile
+++ b/editors/Makefile
@@ -12,7 +12,7 @@
 endif
 srcdir=$(top_srcdir)/editors
 EDITOR_DIR:=./
-include $(top_builddir)/Rules.mak
+include $(top_srcdir)/Rules.mak
 include $(top_builddir)/.config
 include $(srcdir)/Makefile.in
 all: $(libraries-y)