tests: propagate $(TAR) down from the toplevel Makefile

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -1212,6 +1212,7 @@ GIT-CFLAGS: .FORCE-GIT-CFLAGS
 
 GIT-BUILD-OPTIONS: .FORCE-GIT-BUILD-OPTIONS
 	@echo SHELL_PATH=\''$(SHELL_PATH_SQ)'\' >$@
+	@echo TAR=\''$(subst ','\'',$(TAR))'\' >>$@
 
 ### Detect Tck/Tk interpreter path changes
 ifndef NO_TCLTK

t/t5000-tar-tree.sh

@@ -25,7 +25,6 @@ commit id embedding:
 '
 
 . ./test-lib.sh
-TAR=${TAR:-tar}
 UNZIP=${UNZIP:-unzip}
 
 SUBSTFORMAT=%H%n