And here's the error I get when attempting to build it:

--8<---------------cut here---------------start------------->8---
@ build-succeeded /gnu/store/6qcm0pxqhi4hd4lldixdlm88zakl4cip-android-udev-rules-20170910-checkout.drv -
@ build-started /gnu/store/kfdc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv - x86_64-linux /var/log/guix/drvs/kf//dc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv.bz2
ERROR: In procedure primitive-load:
ERROR: In procedure scm_lreadr: /gnu/store/kkrin9p4xd7j4pkiy8rvhq7hlhb5i8kp-android-udev-rules-20170910-guile-builder:1:10: Unknown # object: #\<
builder for `/gnu/store/kfdc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv' failed with exit code 1
@ build-failed /gnu/store/kfdc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv - 1 builder for `/gnu/store/kfdc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv' failed with exit code 1
guix build: error: build failed: build of `/gnu/store/kfdc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv' failed
--8<---------------cut here---------------end--------------->8---

Possibly, the gexps are not being lowered (compiled) in the generated
builder script. When manually indenting it[1] this builder looks like:

--8<---------------cut here---------------start------------->8---
(begin #<gexp
       (begin (use-modules (guix build utils))
	      (install-file "51-android.rules"
			    (string-append #<gexp-output out> "/lib/udev/rules.d"))) 286c810>
			    (define %output (getenv "out"))
			    (define %outputs (map (lambda (o) (cons o (getenv o))) (quote ("out"))))
			    (define %build-inputs (quote (("source" . "/gnu/store/n9prv51xsahbxiz1jypaz6q14gid9r5d-android-udev-rules-20170910-checkout"))))
			    (unsetenv "GUILE_LOAD_COMPILED_PATH")
			    (unsetenv "LD_LIBRARY_PATH"))
(exit (#<gexp
       (begin (use-modules (guix build utils))
	      (install-file "51-android.rules"
			    (string-append #<gexp-output out> "/lib/udev/rules.d"))) 286c810>))
--8<---------------cut here---------------end--------------->8---

It seems to me that the gexp objects should have been lowered into
absolute file paths at this point, no?

Maxim

[1]  A Guile auto-formatter could be an interesting pet project... :)