I can reproduce the issue Tomáš Čech (Sleep_Walker) reported at IRC,
but only when reconfigure under 'pre-inst-env' and without 'gnu/system/linux.go':

$ cd guix; make clean-go
# .../guix/pre-inst-env guix system reconfigure config.scm

;;; Failed to autoload make-session in (gnutls):
;;; ERROR: missing interface for module (gnutls)
;;; Failed to autoload connection-end/client in (gnutls):
;;; ERROR: missing interface for module (gnutls)
;;; Failed to autoload make-session in (gnutls):
;;; ERROR: missing interface for module (gnutls)
The following derivations will be built:
   /gnu/store/8576w1km2a8ij7k66k6n37gyhxzpxda4-system.drv
   /gnu/store/8jg5iqrd04hj1k8nx6fzcm9lz16nmk4r-grub.cfg.drv
   /gnu/store/d53lbndj9yryrzgb3p4vjlb9gyh1rri0-activate.drv
   /gnu/store/y3i8spghyv4dg8d8yl78bvkjb3xcbarb-boot.drv
   /gnu/store/mrlw80nawfbc8mhq3pz6gbxxpgjbabij-pam.d.drv
   /gnu/store/sf3n6ijagmc64ik7mn96p8c69xk30nmv-etc.drv
Backtrace:
In ice-9/boot-9.scm:
 157: 10 [catch #t #<catch-closure e365c0> ...]
In unknown file:
   ?: 9 [apply-smob/1 #<catch-closure e365c0>]
In ice-9/boot-9.scm:
  63: 8 [call-with-prompt prompt0 ...]
In ice-9/eval.scm:
 432: 7 [eval # #]
In ice-9/boot-9.scm:
2401: 6 [save-module-excursion #<procedure e53980 at ice-9/boot-9.scm:4045:3 ()>]
4050: 5 [#<procedure e53980 at ice-9/boot-9.scm:4045:3 ()>]
1724: 4 [%start-stack load-stack #<procedure e66ae0 at ice-9/boot-9.scm:4041:10 ()>]
1729: 3 [#<procedure e6af00 ()>]
In unknown file:
   ?: 2 [primitive-load "/gnu/store/dmsgr6bsp9k0x7c2dmcvhqrgrqqal7kb-pam.d-builder"]
In ice-9/boot-9.scm:
 775: 1 [for-each #<procedure eec7e0 at ice-9/eval.scm:416:20 (a)> (# # # # ...)]
In unknown file:
   ?: 0 [symlink "/gnu/store/pn2wmdczwcknksxhdn4jl6sh49h0vidm-login" ...]

ERROR: In procedure symlink:
ERROR: In procedure symlink: File exists
builder for `/gnu/store/mrlw80nawfbc8mhq3pz6gbxxpgjbabij-pam.d.drv' failed with exit code 1
cannot build derivation `/gnu/store/sf3n6ijagmc64ik7mn96p8c69xk30nmv-etc.drv': 1 dependencies couldn't be built
cannot build derivation `/gnu/store/8576w1km2a8ij7k66k6n37gyhxzpxda4-system.drv': 1 dependencies couldn't be built
killing process 2317
guix system: error: build failed: build of `/gnu/store/8576w1km2a8ij7k66k6n37gyhxzpxda4-system.drv' failed


the pam.d-builder contains duplicates login entries
(I have 3 mingetty-service)