Log Message:
Fix `Fix build on SunOS`.

Passing LIBS=-liconv will be result in unwanted libiconv linkage for libdatrie
(it is just required for trietool-0.2),
then it cause build failure of depending packages due to missing libiconv.

Passing sufficient iconv library to configure script with right way,
and it also fix build failure on other platforms for the case GNU iconv
from pkgsrc is preferred rather than builtin iconv.