WIP: Modify `cmake/FindIconv.cmake` in order to reduce cmake warnings#178

lemniscati wants to merge 7 commits intofukuchi:cygwin-supportfukuchi/libqrencode:cygwin-supportfrom

cygwin-lem:cygwin-support_FindIconv_cmakecygwin-lem/libqrencode:cygwin-support_FindIconv_cmakeCopy head branch name to clipboard