common.mk is NOT working with /bin/sh anymore

at least on Ubuntu.

The brace expansion does not work on Ubuntu /bin/sh (dash), and so
4c0e21add7 effectively broke /bin/sh
compatibility of common.mk.
I guess he was using macOS whose /bin/sh is bash.

Makefile.in

@@ -1,6 +1,6 @@
 # -*- mode: makefile-gmake; indent-tabs-mode: t -*-
 
-SHELL = /bin/sh
+SHELL = /bin/bash
 NULLCMD = @NULLCMD@
 n=$(NULLCMD)
 ECHO1 = $(V:1=$n)