Make the extension manual format using the Makefile; recent changes broke
the dependency information.
diff --git a/Doc/Makefile.deps b/Doc/Makefile.deps
index 3b666f4..967a5f9 100644
--- a/Doc/Makefile.deps
+++ b/Doc/Makefile.deps
@@ -56,7 +56,7 @@
 EXTFILES= ext/ext.tex $(MANSTYLES) $(INDEXSTYLES) $(COMMONTEX) \
 	ext/extending.tex \
 	ext/newtypes.tex \
-	ext/unix.tex \
+	ext/building.tex \
 	ext/windows.tex \
 	ext/embedding.tex \
 	texinputs/reportingbugs.tex