Add -c flag to install to keep it from deleting source on some platforms.

man/Makefile

@@ -1,7 +1,7 @@
 # Makefile
 
 INSTALL= install
-INSTALL_PROGRAM= $(INSTALL)
+INSTALL_PROGRAM= $(INSTALL) -c
 INSTALL_DATA= $(INSTALL) -m 644
 GROFF= groff
 

tools/Makefile

@@ -10,7 +10,7 @@ clean:
 	rm -f $(TARGETS)
 	rm -f *.o
 
-INSTALL= install
+INSTALL= install -c
 INSTALL_PROGRAM= $(INSTALL)
 INSTALL_DATA= $(INSTALL) -m 644