Fix error message printing from Emit

[gretay-js]

Correctly handle exceptions raised during Emit.end_assembly and not only during Emit.funcdecl.

When compiling a function that results in a large frame (for the current frametable format), we were getting unhelpful error messages that look like this:

Fatal error: exception Emitaux.Error(_)
Raised at Emitaux.emit_frames.efa_16_checked in file "backend/emitaux.ml", line 190, characters 9-47
Called from Emitaux.emit_frames.emit_frame in file "backend/emitaux.ml", line 205, characters 4-45
Called from Stdlib__List.iter in file "list.ml", line 114, characters 12-15
Called from Emitaux.emit_frames in file "backend/emitaux.ml", line 283, characters 2-41
Called from Emit.end_assembly in file "backend/amd64/emit.mlp", line 1655, characters 2-931
Called from Asmgen.compile_unit.(fun) in file "backend/asmgen.ml", line 450, characters 12-18
...

With this PR, we will get a slightly nicer user error like this:

File "owl_lapacke_bindings.ml", line 1:
    Error: Error producing assembly code for owl_lapacke_bindings.ml: stack frame too large (136785 bytes)
    - exit external/owl/src/owl/bindings bin_prefix_owl_cblas_parser__Owl_lapacke_bindings.cmx, 5.321s, exited with code 2

(when compiling the file with -linscan).

The error handling was introduced in ocaml/ocaml#10085 for emit_frame (which is actually called during Emit.end_assembly), so this PR is also needed upstream.

I'm trying to move the check itself from emit_frame to record_frame_descr, so the user error can include have a function name as intended, but this PR is independently useful, as we may want to have other user error messages in the future.