net/asterisk-11.x and net/asterisk-13.x: fix menuselect build

net/asterisk-11.x and net/asterisk-13.x: fix menuselect build

- Include host-build.mk, otherwise $HOST_CONFIGURE_ARGS will be empty.
- Remove --with-ncurses=PATH as the PATH is wrong. The ncurses host
  package does not install anything but 'tic'.
- Use $HOSTCC to compile menuselect. This has the added bonus of using
  ccache (if selected).
- Run configure with an unset $CONFIG_SITE so that it doesn't pick a
  cross-compile site-script, e.g. for mips.
- Drop '-lxml2' from $LDFLAGS as the menuselect Makefile will add it
  anyway.
- Move the variables in front of 'make' as they're not arguments.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>