Use @__CWD__@ as the magic string meaning "this directory"

in crunch.conf -- the previous choice, CWD, was too subject to false
matches (this string will be replaced by the absolute pathname
during the build process).

release/picobsd/build/Makefile.conf

@@ -52,4 +52,4 @@ ${BUILDDIR}/crunch.mk: ${BUILDDIR}/crunch1.conf
 
 ${BUILDDIR}/crunch1.conf: ${MY_TREE}/crunch.conf
 	(cd ${BUILDDIR}/crunch ; cat ${.OODATE} | \
-	    sed -e "s@/usr/src@${SRC}@" -e "s@CWD@${MY_TREE}@" > ${.TARGET} )
+	    sed -e "s@/usr/src@${SRC}@" -e "s+@__CWD__@+${MY_TREE}@" > ${.TARGET} )