* gnu/packages/aux-files/run-in-namespace.c (exec_with_proot): New
function.
(main): When 'clone' fails, call 'rm_rf'.
[PROOT_PROGRAM]: When 'clone' fails, call 'exec_with_proot'.
* guix/scripts/pack.scm (wrapped-package): Add #:proot?.
[proot]: New procedure.
[build]: Compile with -DPROOT_PROGRAM when PROOT? is true.
* guix/scripts/pack.scm (%options): Set the 'relocatable?' value to
'proot when "-R" is passed several times.
(guix-pack): Pass #:proot? to 'wrapped-package'.
* tests/guix-pack-relocatable.sh: Use "-RR" on Intel systems that lack
user namespace support.
* doc/guix.texi (Invoking guix pack): Document -RR.
* 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.
