bug#55657: libgccjit is unusable

[Liliana Marie Prikler <liliana.prikler@gmail.com>]

Hi Guix,

with the release of Emacs 28.1, there has been some demand to enable
native-compilation.  While trying to set that up, I've come to realize
that no matter how I slice it, I can't make libgccjit usable.

My test:

$ cd /tmp
$ # fetch the "Hello World" [1] and insert it into gccjit-test.c
$ guix shell --pure gcc-toolchain@9 libgccjit@9 -- \
  gcc gccjit-test.c -o gccjit-test -lgccjit
$ ./gccjit-test
x86_64-unknown-linux-gnu-gcc-9.4.0: fatal error: cannot execute 'as':
execvp: No such file or directory
compilation terminated.

Welp, okay, so maybe testing gccjit outside of its installation does
not work.  What if we try it inside the shell (we can always propagate
libgccjit, no?)

guix shell gcc-toolchain@9 libgccjit@9 -- ./gccjit-test            
ld: cannot find crtbeginS.o: Datei oder Verzeichnis nicht gefunden
ld: cannot find -lgcc
ld: cannot find -lgcc
collect2: Fehler: ld gab 1 als Ende-Status zurück
libgccjit.so: error: error invoking gcc driver
NULL result

For the record, Emacs 28 fails with a different error during
configuration, though interestingly they use a smaller program and
appear to omit -lgccjit.
./conftest: error while loading shared libraries: libgccjit.so.0:
cannot open shared object file: No such file or directory

I'm at a loss.  Is there any way to make libgccjit actually usable?

[1] https://gcc.gnu.org/onlinedocs/jit/intro/tutorial01.html