* distro/patches/guile-relocatable.patch: Change to use /proc/self/exe
instead of PROGRAM_INVOCATION_NAME. Useful because Nix itself passes
just the basename of builders that it executes.
* distro/packages/base.scm (%guile-static, %guile-static-stripped): New
variables.
* distro/patches/guile-relocatable.patch: New file.
* Makefile.am (dist_patch_DATA): Add it.