modinfo: lookup compile_commands.json by object

modinfo: lookup compile_commands.json by object

Since modinfo support was added, Meson fixed several issues with
extract_objects and compile_commands.json lookups can be simplified.
If the lookup uses the object file as key, there is no need to use the
command line to distinguish among all entries for a given source.

Ninja 1.9 is required in order to produce the 'output' key in
compile_commands.json; it is available in CentOS Stream 9, Debian 11, SLES
15.2, Ubuntu 20.04 and in all recent BSD distros.  Samurai also has it.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>