% CC=clang CXX=clang++ ./configure --enable-optimizations --with-lto
checking build system type... x86_64-apple-darwin16.7.0
checking host system type... x86_64-apple-darwin16.7.0
checking for python3.10... no
checking for python3... python3
checking for --enable-universalsdk... no
checking for --with-universal-archs... no
checking MACHDEP... "darwin"
checking for gcc... clang
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables... 
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether clang accepts -g... yes
checking for clang option to accept ISO C89... none needed
checking how to run the C preprocessor... clang -E
checking for grep that handles long lines and -e... /usr/bin/grep
checking for a sed that does not truncate output... /usr/local/bin/sed
checking for --with-cxx-main=<compiler>... no
checking for the platform triplet based on compiler characteristics... darwin
configure: error: internal configure error for the platform triplet, please file a bug report

The problem occurs here at line 5382 of configure:

if test x$PLATFORM_TRIPLET != x && test x$MULTIARCH != x; then
  if test x$PLATFORM_TRIPLET != x$MULTIARCH; then
    as_fn_error $? "internal configure error for the platform triplet, please file a bug report" "$LINENO" 5
  fi

The problem is that $PLATFORM_TRIPLET is set to darwin (which appears to be correct) and $MULTIARCH is set thus:

MULTIARCH=$($CC --print-multiarch 2>/dev/null)

which evaluates to x86_64-apple-darwin16.7.0.

This is with the public llvm / clang version 13.0.0.

If you set MULTIARCH=darwin in configure, python configures, builds and runs.