Cross-building bootstrap binaries fail in current master

[csanchezdll@gmail.com (Carlos Sánchez de La Lama)]

Hi all,

with current master (1dc30f92320c5e1b528a7eec2b0a4ce529f70c56), trying

guix build --target=i686-linux bootstrap-tarballs

fails with

--8<---------------cut here---------------start------------->8---
starting phase `unpack'
In execvp of tar: No such file or directory
phase `unpack' failed after 0.0 seconds
builder for
`/gnu/store/cyr61arxvjxdaxgy8rk8rzibyi2hg3pq-make-boot0-4.2.drv' failed
with exit code 1
@ build-failed
/gnu/store/cyr61arxvjxdaxgy8rk8rzibyi2hg3pq-make-boot0-4.2.drv - 1
builder for
`/gnu/store/cyr61arxvjxdaxgy8rk8rzibyi2hg3pq-make-boot0-4.2.drv' failed
with exit code 1
cannot build derivation
`/gnu/store/s3ax042hlvymvl749hksalir695vphjm-gcc-cross-boot0-4.9.3.drv':
1 dependencies couldn't be built
guix build: error: build failed: build of
`/gnu/store/s3ax042hlvymvl749hksalir695vphjm-gcc-cross-boot0-4.9.3.drv'
failed
--8<---------------cut here---------------end--------------->8---

This used to work previously (like couple of weeks ago). Unfortunately,
I updated my all my branches to send last patches, so I am not sure
which commit I was using before.

Apparently, guile fails to execvp "tar".

Seems related to this:
https://lists.gnu.org/archive/html/guix-devel/2015-01/msg00162.html

Any clues?

BR

Carlos