s/SHELL/SHELL_PATH/ in Makefile

With the current Makefile we don't use the shell chosen by the
platform specific defines when we invoke GIT-VERSION-GEN.

Signed-off-by: Fredrik Kuivinen <freku045@student.liu.se>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Makefile

@@ -67,7 +67,7 @@ all:
 # change being considered an inode change from the update-cache perspective.
 
 GIT-VERSION-FILE: .FORCE-GIT-VERSION-FILE
-	@$(SHELL) ./GIT-VERSION-GEN
+	@$(SHELL_PATH) ./GIT-VERSION-GEN
 -include GIT-VERSION-FILE
 
 # CFLAGS and LDFLAGS are for the users to override from the command line.