LIB: Allow building of the shared library to be suppressed

Allow building of the shared library to be suppressed by passing NO_SOLIB=1 to
the Makefile.

Reported-and-tested-by: Vicente Olivert Riera <vincent.riera@imgtec.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Don't define LNS twice in the Makefile and define in terms of $(LN)

The LNS Makefile macro is defined the same way twice.  Remove the second
definition.  Also, put the definition of LNS in terms of $(LN).

Signed-off-by: David Howells <dhowells@redhat.com>
Define LN as it isn't defined by make and use $(LNS) for a couple of ln -sf

Define LN as it isn't defined by make, but LNS is now defined in terms of it.

Also, use $(LNS) for a couple of "ln -sf" commands.

Signed-off-by: David Howells <dhowells@redhat.com>