Launch the bourne shell using "sh" rather than "${SHELL}", as the latter

may come in from the environment and reflect the user's interactive shell.
Using bare "sh" is the dominant pattern in existing makefiles.

MFC this together with r255775.

Approved by:	re ()
MFC after:	2 weeks

include/Makefile

@@ -113,7 +113,7 @@ osreldate.h vers.c: ${NEWVERS_SH} ${PARAM_H} ${MK_OSRELDATE_SH}
 	    MAKE="${MAKE}" \
 	    NEWVERS_SH=${NEWVERS_SH} \
 	    PARAM_H=${PARAM_H} \
-	    ${SHELL} ${MK_OSRELDATE_SH}
+	    sh ${MK_OSRELDATE_SH}
 
 .for i in ${LHDRS}
 INCSLINKS+=	sys/$i ${INCLUDEDIR}/$i