Determining if the function smtp_create_session exists in the esmtp failed with the following output:
Change Dir: /usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/log4cxx-0.12.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/gmake cmTC_8af32/fast && gmake[1]: Entering directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/log4cxx-0.12.0/CMakeFiles/CMakeTmp'
/usr/bin/gmake  -f CMakeFiles/cmTC_8af32.dir/build.make CMakeFiles/cmTC_8af32.dir/build
gmake[2]: Entering directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/log4cxx-0.12.0/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_8af32.dir/CheckFunctionExists.cxx.o
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/bin/s390x-buildroot-linux-gnu-g++ --sysroot=/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/s390x-buildroot-linux-gnu/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -g0 -D_FORTIFY_SOURCE=1 -DCHECK_FUNCTION_EXISTS=smtp_create_session  -DNDEBUG   -std=c++17 -o CMakeFiles/cmTC_8af32.dir/CheckFunctionExists.cxx.o -c /usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/log4cxx-0.12.0/CMakeFiles/CheckLibraryExists/CheckFunctionExists.cxx
Linking CXX executable cmTC_8af32
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_8af32.dir/link.txt --verbose=1
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/bin/s390x-buildroot-linux-gnu-g++ --sysroot=/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/s390x-buildroot-linux-gnu/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -g0 -D_FORTIFY_SOURCE=1 -DCHECK_FUNCTION_EXISTS=smtp_create_session  -DNDEBUG    CMakeFiles/cmTC_8af32.dir/CheckFunctionExists.cxx.o  -o cmTC_8af32  -lesmtp 
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/lib/gcc/s390x-buildroot-linux-gnu/10.3.0/../../../../s390x-buildroot-linux-gnu/bin/ld: cannot find -lesmtp
collect2: error: ld returned 1 exit status
gmake[2]: *** [cmTC_8af32] Error 1
gmake[2]: Leaving directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/log4cxx-0.12.0/CMakeFiles/CMakeTmp'
gmake[1]: *** [cmTC_8af32/fast] Error 2
gmake[1]: Leaving directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/log4cxx-0.12.0/CMakeFiles/CMakeTmp'