* gnu/packages/aux-files/run-in-namespace.c (write_id_map)
(disallow_setgroups): New functions.
(main): Use 'clone' via 'syscall' instead of 'fork' followed by
'unshare'. Add calls to 'disallow_setgroups' and 'write_id_map' in the
parent process.
* gnu/packages/aux-files/run-in-namespace.c: New file.
* Makefile.am (AUX_FILES): Add it.
* guix/scripts/pack.scm (<c-compiler>): New record type.
(c-compiler, bootstrap-c-compiler, c-compiler-compiler): New procedures.
(self-contained-tarball): Use
'relative-file-name' for the SOURCE -> TARGET symlink.
(docker-image): Add 'defmod' to please Geiser.
(wrapped-package, map-manifest-entries): New procedures.
(%options, show-help): Add --relocatable.
(guix-pack): Honor it.
