>> .SHELL: name=sh path=/usr/xpg4/bin/sh
>
>Note that this has to be done for every Makefile and I would go as far

Actually you'd just put it in sys.mk or rather SunOS.sys.mk

But as I mentioned earlier, I've posted bmake-20071011 which overhauls
the defshell handling in configure and uses /usr/xpg4/bin/sh by default 
on SunOS.