build failed if -DUSE_ICONV=ON is given

Reproduction steps

curl -LO https://github.com/libgit2/libgit2/archive/v1.5.1.tar.gz
tar vxf v1.5.1.tar.gz
cd libgit2-1.5.1

cmake \
    -S . \
    -B build.d \
    -DBUILD_TESTS=OFF \
    -DBUILD_EXAMPLES=OFF \
    -DBUILD_SHARED_LIBS=OFF \
    -DUSE_SSH=OFF \
    -DUSE_ICONV=ON \
    -DUSE_HTTPS=OpenSSL \
    -DREGEX_BACKEND=pcre2 \
    -DCMAKE_FIND_ROOT_PATH='/home/leleliu008/.ppkg/installed/openssl;/home/leleliu008/.ppkg/installed/pcre2;/home/leleliu008/.ppkg/installed/zlib;/home/leleliu008/.ppkg/installed/libiconv' \
    -DCMAKE_C_FLAGS=-I/home/leleliu008/.ppkg/installed/openssl/include \
    -DCMAKE_VERBOSE_MAKEFILE=ON \
    -DCMAKE_FIND_DEBUG_MODE=ON \
    -DCMAKE_FIND_USE_CMAKE_PATH=ON \
    -DCMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH=OFF \
    -DCMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH=OFF \
    -DCMAKE_FIND_USE_CMAKE_SYSTEM_PATH=OFF \
    -DCMAKE_FIND_USE_INSTALL_PREFIX=OFF \
    -DCMAKE_INCLUDE_PATH=/include \
    -DCMAKE_LIBRARY_PATH=/lib \
    -DCMAKE_PROGRAM_PATH='/bin;/sbin'
cmake --build build.d

Expected behavior

ca be successfully built.

Actual behavior

/usr/bin/ld: ../util/CMakeFiles/util.dir/fs_path.c.o: in function `git_fs_path_iconv_init_precompose':
/home/leleliu008/tmp/tmp.d/tmp.d/libgit2-1.5.1/src/util/fs_path.c:982: undefined reference to `libiconv_open'
/usr/bin/ld: ../util/CMakeFiles/util.dir/fs_path.c.o: in function `git_fs_path_iconv_clear':
/home/leleliu008/tmp/tmp.d/tmp.d/libgit2-1.5.1/src/util/fs_path.c:990: undefined reference to `libiconv_close'
/usr/bin/ld: ../util/CMakeFiles/util.dir/fs_path.c.o: in function `git_fs_path_iconv':
/home/leleliu008/tmp/tmp.d/tmp.d/libgit2-1.5.1/src/util/fs_path.c:1015: undefined reference to `libiconv'
collect2: error: ld returned 1 exit status
gmake[2]: *** [src/cli/CMakeFiles/git2_cli.dir/build.make:596: git2_cli] Error 1
gmake[2]: Leaving directory '/home/leleliu008/tmp/tmp.d/tmp.d/libgit2-1.5.1/build.d'
gmake[1]: *** [CMakeFiles/Makefile2:326: src/cli/CMakeFiles/git2_cli.dir/all] Error 2
gmake[1]: Leaving directory '/home/leleliu008/tmp/tmp.d/tmp.d/libgit2-1.5.1/build.d'
gmake: *** [Makefile:139: all] Error 2

cmake-config.log
cmake-build.log

Version of libgit2 (release number or SHA1)

https://github.com/libgit2/libgit2/archive/v1.5.1.tar.gz

Operating system(s) tested

ubuntu-22.10

more

I noticed that cmake config log say Found Iconv: provided by libc, this is not correct, I using a seperate libiconv, I do not use the iconv functions in libc. It seems that libiconv.so was not linked into the git2 due to it was expected to be provided by libc but actually it was in a seperate library.

Start by reproducing the CMake configuration with USE_ICONV=ON and inspect the Iconv detection and link settings, then review src/util/fs_path.c around the reported iconv calls. Done means the libgit2 build succeeds when iconv is supplied as a separate libiconv library rather than provided by libc.