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_0f1e9/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_0f1e9.dir/build.make CMakeFiles/cmTC_0f1e9.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_0f1e9.dir/CheckFunctionExists.cxx.o
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/bin/mips64el-linux-g++ --sysroot=/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/mips64el-buildroot-linux-uclibc/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -g0 -DCHECK_FUNCTION_EXISTS=smtp_create_session  -DNDEBUG   -std=c++17 -o CMakeFiles/cmTC_0f1e9.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_0f1e9
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_0f1e9.dir/link.txt --verbose=1
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/bin/mips64el-linux-g++ --sysroot=/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/mips64el-buildroot-linux-uclibc/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -g0 -DCHECK_FUNCTION_EXISTS=smtp_create_session  -DNDEBUG    CMakeFiles/cmTC_0f1e9.dir/CheckFunctionExists.cxx.o  -o cmTC_0f1e9  -lesmtp 
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/mips64el-buildroot-linux-uclibc/8.4.0/../../../../mips64el-buildroot-linux-uclibc/bin/ld: cannot find -lesmtp
collect2: error: ld returned 1 exit status
gmake[2]: *** [cmTC_0f1e9] 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_0f1e9/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'