[libcxx] Use debug() instead of note() for substitutions (#193667)
This reduces the noise in the lit output when running tests like this:
```
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libunwind-shared.cfg.in) Using %{cxx} substitution: 'bin/clang++'
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libunwind-shared.cfg.in) Using %{flags} substitution: ' --target=x86_64-unknown-linux-gnu'
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libunwind-shared.cfg.in) Using %{compile_flags} substitution: '-nostdinc++ -I %{include} -D_LIBUNWIND_HAVE_GETAUXVAL -funwind-tables -std=c++26 -Werror -Wall -Wctad-maybe-unsupported -Wextra -Wshadow -Wundef -Wunused-template -Wno-unused-command-line-argument -Wno-attributes -Wno-pessimizing-move -Wno-noexcept-type -Wno-atomic-alignment -Wno-reserved-module-identifier -Wdeprecated-copy -Wdeprecated-copy-dtor -Wshift-negative-value -Wno-user-defined-literals -Wno-tautological-compare -Wsign-compare -Wunused-variable -Wunused-parameter -Wunreachable-code -Wno-unused-local-typedef -Wno-local-type-template-args -Wno-c++11-extensions -Wno-unknown-pragmas -Wno-pass-failed -Wno-mismatched-new-delete -Wno-redundant-move -Wno-self-move -Wno-nullability-completeness -flax-vector-conversions=none -D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -Wuser-defined-warnings'
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libunwind-shared.cfg.in) Using %{link_flags} substitution: '-L %{lib} -Wl,-rpath,%{lib} -lunwind -Wl,--export-dynamic -ldl -latomic'
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libunwind-shared.cfg.in) Using %{benchmark_flags} substitution: ''
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libunwind-shared.cfg.in) Using %{exec} substitution: '%{executor} --execdir %{temp} -- '
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libunwind-shared.cfg.in) All available features: add-latomic-workaround, buildhost=linux, c++26, can-create-symlinks, character-conversion-warnings, clang, clang-23, clang-23.0, clang-23.0.0, diagnose-if-support, enable-benchmarks=run, gcc-style-warnings, has-fblocks, has-fconstexpr-steps, has-filecheck, has-unix-headers, host-has-gdb-with-python, large_tests, libcpp-has-no-experimental-hardening-observe-semantic, libcpp-has-no-experimental-optional-iterator, libcpp-has-no-experimental-syncstream, libcpp-has-no-experimental-tzdb, libcpp-has-no-incomplete-pstl, linux, locale.cs_CZ.ISO8859-2, locale.en_US.UTF-8, locale.fr_CA.ISO8859-1, locale.fr_FR.UTF-8, locale.ja_JP.UTF-8, locale.ru_RU.UTF-8, locale.zh_CN.UTF-8, long_tests, objcopy-available, objective-c++, optimization=none, std-at-least-c++03, std-at-least-c++11, std-at-least-c++14, std-at-least-c++17, std-at-least-c++20, std-at-least-c++23, std-at-least-c++26, stdlib=libc++, stdlib=llvm-libc++, target=x86_64-unknown-linux-gnu, verify-support, win32-broken-utf8-wchar-ctype
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libc++-shared.cfg.in) Using %{cxx} substitution: 'bin/clang++'
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libc++-shared.cfg.in) Using %{flags} substitution: '-pthread --target=x86_64-unknown-linux-gnu'
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libc++-shared.cfg.in) Using %{compile_flags} substitution: '-nostdinc++ -I %{target-include-dir} -I %{include-dir} -I %{libcxx-dir}/test/support -std=c++26 -Werror -Wall -Wctad-maybe-unsupported -Wextra -Wshadow -Wundef -Wunused-template -Wno-unused-command-line-argument -Wno-attributes -Wno-pessimizing-move -Wno-noexcept-type -Wno-atomic-alignment -Wno-reserved-module-identifier -Wdeprecated-copy -Wdeprecated-copy-dtor -Wshift-negative-value -Wno-user-defined-literals -Wno-tautological-compare -Wsign-compare -Wunused-variable -Wunused-parameter -Wunreachable-code -Wno-unused-local-typedef -Wno-local-type-template-args -Wno-c++11-extensions -Wno-unknown-pragmas -Wno-pass-failed -Wno-mismatched-new-delete -Wno-redundant-move -Wno-self-move -Wno-nullability-completeness -flax-vector-conversions=none -D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -D_LIBCPP_ENABLE_EXPERIMENTAL -Wuser-defined-warnings'
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libc++-shared.cfg.in) Using %{link_flags} substitution: '-lc++experimental -nostdlib++ -L %{lib-dir} -Wl,-rpath,%{lib-dir} -lc++ -latomic'
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libc++-shared.cfg.in) Using %{benchmark_flags} substitution: '-I runtimes/runtimes-bins/libcxx/test/benchmarks/google-benchmark/include -L runtimes/runtimes-bins/libcxx/test/benchmarks/google-benchmark/lib -L runtimes/runtimes-bins/libcxx/test/benchmarks/google-benchmark/lib64 -l benchmark'
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libc++-shared.cfg.in) Using %{exec} substitution: '%{executor} --execdir %{temp} -- '
llvm-lit: llvm-project/libcxx/utils/libcxx/test/config.py:24: note: (llvm-libc++-shared.cfg.in) All available features: add-latomic-workaround, buildhost=linux, c++26, c++experimental, can-create-symlinks, character-conversion-warnings, clang, clang-23, clang-23.0, clang-23.0.0, diagnose-if-support, enable-benchmarks=no, gcc-style-warnings, has-1024-bit-atomics, has-64-bit-atomics, has-fblocks, has-fconstexpr-steps, has-filecheck, has-unix-headers, host-has-gdb-with-python, large_tests, libcpp-abi-version=1, libcpp-hardening-mode=extensive, libcpp-has-no-availability-markup, libcpp-has-thread-api-pthread, linux, locale.cs_CZ.ISO8859-2, locale.en_US.UTF-8, locale.fr_CA.ISO8859-1, locale.fr_FR.UTF-8, locale.ja_JP.UTF-8, locale.ru_RU.UTF-8, locale.zh_CN.UTF-8, objective-c++, optimization=none, std-at
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