bug#30124: "guix pull" broken on master

[Danny Milosavljevic]

First: ok:

$ guix pull
Updating from Git repository at 'https://git.savannah.gnu.org/git/guix.git'...
Building from Git commit 15eef66e5d7e82a467dd7fbf2e72f7d1fcd6c26f...
guix pull: warning: failed to load '(wip pascal)':
ERROR: Unbound variable: custom-gccx
The following derivation will be built:
   /gnu/store/pas9dr7m0wl3af486zasm1q82j5s62g3-guix-latest.drv
copying and compiling to 
'/gnu/store/cl45yzn7c7bc3gqgy94isai5n5allk2v-guix-latest' with Guile 2.2.2...
loading...       26.2% of 661 filesrandom seed for tests: 1516016025
compiling...    100.0% of 661 files

Some deprecated features have been used.  Set the environment
variable GUILE_WARN_DEPRECATED to "detailed" and rerun the
program to get more information.  Set it to "no" to suppress
this message.
updated GNU Guix successfully deployed under `/home/dannym/.config/guix/latest'

Second: broken:

$ guix pull
Updating from Git repository at 'https://git.savannah.gnu.org/git/guix.git'...
Building from Git commit dd72837dff128dbb1258826fe39467d1ef000ac1...
The following derivation will be built:
   /gnu/store/cf9cp4nwqgig5ngf7hh5h2r0i3cag181-guix-latest.drv
copying and compiling to 
'/gnu/store/61ljfph5g51pl8vb2ryc5b5cwpycab7j-guix-latest' with Guile 2.2.2...
loading...       26.2% of 661 filesrandom seed for tests: 1516019897
compiling...    100.0% of 661 files
Backtrace:
Exception thrown while printing backtrace:
ERROR: In procedure private-lookup: Module named (guile) does not exist
Some deprecated features have been used.  Set the environment
variable GUILE_WARN_DEPRECATED to "detailed" and rerun the
program to get more information.  Set it to "no" to suppress
this message.
builder for `/gnu/store/cf9cp4nwqgig5ngf7hh5h2r0i3cag181-guix-latest.drv' 
failed with exit code 1
guix pull: error: build failed: build of 
`/gnu/store/cf9cp4nwqgig5ngf7hh5h2r0i3cag181-guix-latest.drv' failed