Failing buildword due to execution permission (with fix)

[Simon J. Gerraty]

> >> include/Makefile:MK_OSRELDATE_SH=       ${.CURDIR}/mk-osreldate.sh
> >> include/Makefile:           sh ${MK_OSRELDATE_SH}
> 
> I actually wrote up a patch recently to use ${SH} in all places of 'sh'
> and '/bin/sh', and noted on SHELL?= that was not useful to use, but did
> not commit it (yet).

We (junos) use HOST_SH I think for this, since if building on a non-native
host, /bin/sh cannot be relied on.
FreeBSD sys.mk already has

__MAKE_SHELL?=/bin/sh

so I guess you could use that.