Correct use of sh if

tests/Makefile.am

@@ -108,8 +108,8 @@ hamlibdatetime.h: FORCE
 	if test -x $(top_srcdir)/.git ; then \
 		echo "/* This date time is from the last non-merge commit to Hamlib. */" > $@.tmp ;\
 		echo "#define HAMLIBDATETIME "\"$$(TZ=UTC git --git-dir=$(top_srcdir)/.git log --no-merges --date='format-local:%a %b %d %H:%M:%S %Y %z SHA=' --format='%cd' -n 1)$$(git --git-dir=$(top_srcdir)/.git log --no-merges | grep commit | head -n 1 | cut -c8-13)\"  >> $@.tmp ;\
-		if test $$(diff $@.tmp $@) ; then \
-			mv $@.tmp $@ ;\
+		if $$(diff $@.tmp $@) ; then \
+			mv -f $@.tmp $@ ;\
 			cp -f $@ $(top_srcdir)/tests/$(@F) ;\
 		fi \
 	fi