Instead of splitting ${ICONV_LIBRARY}'s path and then assuming the
library is called "libiconv.so", use ${ICONV_LIBRARY}'s entire value in
the calls to check_library_exists().
If that is not done, the iconv detection fails if one sets ICONV_LIBRARY
to, for example, /usr/lib/libc.so, as the previous calls would still
pass "-liconv" to the linker instead of the chosen value.
482eeacdeb