@lritter update: it compiles; i just needed to insert:

#elif defined(__APPLE__)
#include <mach-o/dyld.h>

...after line 164 in exepath.inc.

then, using homebrew's build of clang (which is stock LLVM clang as opposed to apple clang):

cd nudl
time /opt/homebrew/opt/llvm/bin/clang++ -std=c++20 -Iinclude ./t.cpp

...where t.cpp contains only:
https://paste.sr.ht/~duangle/0eb1e0eca41be7a00d056bec05962c3835bbe120

and we get:
0.43s user 0.07s system 106% cpu 0.473 total