Compiler diagnostic with clang from the LLVM 9 download package about argparse HOT 2 CLOSED

pranav@ubuntu:~/dev/argparse/build$ export CC=/usr/bin/clang-12
pranav@ubuntu:~/dev/argparse/build$ export CXX=/usr/bin/clang++-12
pranav@ubuntu:~/dev/argparse/build$ cmake -DARGPARSE_BUILD_TESTS=on ..
-- The CXX compiler identification is Clang 12.0.0
-- Check for working CXX compiler: /usr/bin/clang++-12
-- Check for working CXX compiler: /usr/bin/clang++-12 -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- The C compiler identification is Clang 12.0.0
-- Check for working C compiler: /usr/bin/clang-12
-- Check for working C compiler: /usr/bin/clang-12 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/pranav/dev/argparse/build
pranav@ubuntu:~/dev/argparse/build$ make -j20
Scanning dependencies of target ARGPARSE
[  3%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_const_correct.cpp.o
[ 11%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_append.cpp.o
[ 14%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_actions.cpp.o
[ 18%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_compound_arguments.cpp.o
[ 22%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_default_args.cpp.o
[ 25%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_container_arguments.cpp.o
[ 29%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_get.cpp.o
[ 29%] Building CXX object test/CMakeFiles/ARGPARSE.dir/main.cpp.o
[ 37%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_help.cpp.o
[ 40%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_invalid_arguments.cpp.o
[ 40%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_equals_form.cpp.o
[ 44%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_is_used.cpp.o
[ 48%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_issue_37.cpp.o
[ 51%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_negative_numbers.cpp.o
[ 55%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_parent_parsers.cpp.o
[ 59%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_parse_args.cpp.o
[ 62%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_optional_arguments.cpp.o
[ 66%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_prefix_chars.cpp.o
[ 70%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_parse_known_args.cpp.o
[ 74%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_positional_arguments.cpp.o
[ 77%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_repr.cpp.o
[ 81%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_required_arguments.cpp.o
[ 85%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_scan.cpp.o
[ 88%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_subparsers.cpp.o
[ 92%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_value_semantics.cpp.o
[ 96%] Building CXX object test/CMakeFiles/ARGPARSE.dir/test_version.cpp.o
[100%] Linking CXX executable tests
[100%] Built target ARGPARSE
pranav@ubuntu:~/dev/argparse/build$ ./test/tests 
[doctest] doctest version is "2.4.8"
[doctest] run with "--help" for options
===============================================================================
[doctest] test cases: 158 | 158 passed | 0 failed | 1 skipped
[doctest] assertions: 706 | 706 passed | 0 failed |
[doctest] Status: SUCCESS!