build: Force rebuild *.t programs

This makes sure that those programs are always built afresh instead
being stuck at outdated build. This is needed because corresponding test .c
file includes many other .c files and we don't implement dependency tracking.

Makefile

 # Wendelin.core | Instructions to build & test
-# Copyright (C) 2014-2019  Nexedi SA and Contributors.
+# Copyright (C) 2014-2021  Nexedi SA and Contributors.
 #                     	   Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -94,7 +94,7 @@ test.t	: $(TESTS:%=%.trun)
 %.trun	: %.t
 	$(XRUN<)
 
-%.t	: %.c $(ccan_config)
+%.t	: %.c $(ccan_config) FORCE
 	$(LINKC)
 
 # test with AddressSanitizer