configure: fix static linking with readline

configure: fix static linking with readline

When static linking is used, the order of the libraries is important,
and the libraries using a symbol from another library should be listed
*before* the library providing that symbol (see
http://eli.thegreenplace.net/2013/07/09/library-order-in-static-linking)
for details.

When vtysh is linked statically, the command line contains "-lcurses
-lreadline", which causes a build failure due to unresolved
symbols. This is because readline is using symbols from the curses
library: the order should be the opposite.

This patch fixes that problem by putting the -lreadline at the
beginning of the LIBREADLINE variable calcualted by the configure
script.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>