0) rename UNPRIVILEGED UNPRIVED. It was too long. We'll argue about if
we should replace it with yet something else later. It currently
logs metadata by default. We'll argue more about that later too.
1) create a _SRC_TOP_OBJ_ variable pointing at the /usr/src objdir so
we know where to dump metadata.
2) Add a METALOG variable pointing at the default location for the
metadata log. (This may be moved or renamed -- the location is just
for testing.)
3) Add a HOST_INSTALL_FILE used in host tools Makefiles instead of
INSTALL_FILE, which doesn't include ${INSTPRIV} (i.e -U -M ${METALOG})
4) Add INSTALL_LINK, INSTALL_SYMLINK for use in other .mk files so we
can get rid of explicit uses of ln. Slightly clean up INSTALL_FILE.
77bd523e70