configure.in for libiconv ( iconv ) checking.

As the title states, use this with your autoconf and automake under 
both Linux ( where iconv_open() is a libc built-in function ) 
and Solaris ( where iconv_open() is a part of GNU libiconv ).

#
# Checks for iconv
#
AC_MSG_CHECKING([for a usable iconv])
ICONV_LIBS=""
AC_TRY_LINK([#include ],
        [iconv_open ("from", "to");],
        [use_iconv=1],
        [use_iconv=0])
if test x$use_iconv = x1; then
    AC_MSG_RESULT([libc])
else
    # try using libiconv
    fontconfig_save_libs="$LIBS"
    LIBS="$LIBS -liconv"

    AC_TRY_LINK([#include ],
            [iconv_open ("from", "to");],
            [use_iconv=1],
            [use_iconv=0])
   
    if test x$use_iconv = x1; then
        ICONV_LIBS="-liconv"
        AC_MSG_RESULT([libiconv])
    else
        AC_MSG_RESULT([no])
    fi

    LIBS="$fontconfig_save_libs"
fi
AC_SUBST(ICONV_LIBS)
AC_DEFINE_UNQUOTED(USE_ICONV,$use_iconv,[Use iconv.])