Some Common Lisp FFIs have opted to coax this information out of the compiler. https://github.com/rpav/c2ffi is a C++ tool that links to libclang-cpp and literally outputs JSON with sizes and alignments. (It is then used by https://github.com/rpav/cl-autowrap to autogenerate a Lisp wrapper.) The older CFFI Groveller [1] works by generating C code which is compiled by the system C compiler (e.g. GCC or Clang) and, when executed, prints Lisp code that contains resolved values of constants, sizes, alignments, etc.
When you run ./configure or cmake for a C program, it often prints something like "configure: checking size of long long" or "-- Check size of long long". This is done by generating, compiling and running a short C program that prints sizeof long long. The result goes into an autogenerated config.h.
In Rust the first example of build.rs usage [1] compiles and runs a C program during the build of the crate, and the next page [2] shows how to use autogenerated Rust code with include! macro.
Lisp is more similar to C or Rust than you might think. Code generation typically happens while the library or program source code is being loaded, and it is orchestrated by a declaration in an .asd file, which is analogous to meson.build, but looks more like Cargo.toml, e.g. [3]
[1] https://cffi.common-lisp.dev/manual/html_node/The-Groveller....