bug#46256: [feature/native-comp] AOT eln files ignored if run from build tree

[Eli Zaretskii]

> Date: Wed, 03 Mar 2021 20:43:01 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 46256@debbugs.gnu.org, andrewjmoreton@gmail.com
> 
>        Warning (comp): comp.h:70: Emacs fatal error: assertion failed: 
> NATIVE_COMP_UNITP (a)^M
> 
> I also see similar picture in emacs_backtrace.txt:
> 
>   emacs_abort at src/w32fns.c:10947
>   terminate_due_to_signal at src/emacs.c:417
>   die at src/alloc.c:7452
>   XNATIVE_COMP_UNIT at src/comp.h:70
>   load_comp_unit at src/comp.c:4766
>   syms_of_comp at src/comp.c:5077
>   Fload at src/lread.c:1548
> 
> (My Emacs is compiled with --enable-checking=yes.)

I still keep seeing this from time to time, even though I have a local
patch to disable the tree-isolate-paths pass.  Suggestions for
debugging this are welcome.

(I must say that the way the async compilations are run makes it hard
to track down fatal errors, because I don't even have an easy way of
knowing which .el file was being compiled when the crash happened.
Any enhancements of the logging and the diagnostic messages to help in
these matters will be very welcome.  E.g., how about introducing an
intermediate log level that would just show the currently compiled .el
file's name?)