As far as I can tell you're not invoking configure to cross compile.
You told it the target (note: this should really be called host but it
doesn't matter) is arm but you're invoking the compiler as "clang" so
it will just be whatever clang's default target is (probably x86_64).

If you want to cross compile, you need something like
CC="/usr/lib/llvm-13/bin/clang --target=armv7-a" and you also need to
have a suitable compiler-rt for arm available.

We should probably do something to detect this kind of breakage
earlier than at long double type mismatch.

Rich