tools/objtool/Makefile: don't assume sync-check.sh is executable

patch(1) loses the x bit.  So if a user follows our patching
instructions in Documentation/admin-guide/README.rst, their kernel will
not compile.

Fixes: 3bd51c5a ("objtool: Move kernel headers/code sync check to a script")
Reported-by: Nicolas Bock <nicolasbock@gentoo.org>
Reported-by Joakim Tjernlund <Joakim.Tjernlund@infinera.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/objtool/Makefile

@@ -46,7 +46,7 @@ $(OBJTOOL_IN): fixdep FORCE
 	@$(MAKE) $(build)=objtool
 
 $(OBJTOOL): $(LIBSUBCMD) $(OBJTOOL_IN)
-	@./sync-check.sh
+	@$(CONFIG_SHELL) ./sync-check.sh
 	$(QUIET_LINK)$(CC) $(OBJTOOL_IN) $(LDFLAGS) -o $@