gnu-build-system not handling pkg-config properly in package definition

[Nathan Dehnel]

https://www.mail-archive.com/bug-guix@gnu.org/msg00180.html
According to this,  if you use gnu-build-system, all packages added to
inputs get added to PKG_CONFIG_PATH, but for some reason it's not
happening for util-linux, which causes a build error. During the build
PKG_CONFIG_PATH ends up not containing any of the util-linux packages.
Does anyone know how to fix this? Package below:

(define-module (gooby-channel packages bcache-tools)
  #:use-module (guix licenses)
  #:use-module (guix packages)
  #:use-module (gnu packages)
  #:use-module (guix build-system gnu)
  #:use-module (guix git-download)
  #:use-module (gnu packages linux)
  #:use-module (gnu packages pkg-config))

(define-public bcache-tools
  (package
    (name "bcache-tools")
    (version "1.1")
    (source
     (origin
       (method git-fetch)
       (uri
        (git-reference
         (url (string-append
"https://git.kernel.org/pub/scm/linux/kernel/git/colyli/"; name
".git"))
         (commit (string-append name "-" version))))
       (file-name (git-file-name name version))
       (sha256
        (base32
         "1vfqm3asx7h1sjwyq45dki4wk7lkipqrx2pw2hnqm4xir85qf67h"))
       (patches (search-patches "bcache-tools-noprobe.patch"))))
    (build-system gnu-build-system)
    (arguments
     `(;;#:tests? #f                      ; no "check" target
       #:make-flags
         (list (string-append "PREFIX=" (assoc-ref %outputs "out")))
       #:phases
         (modify-phases %standard-phases
          (delete 'configure))))
    (inputs
     `(("util-linux" ,util-linux)))
    (native-inputs
     `(("pkg-config" ,pkg-config)))
    (home-page "https://bcache.evilpiepirate.org/";)
    (synopsis "These are the userspace tools required for bcache.")
    (description "Bcache patches for the Linux kernel allow one to use
SSDs to cache other block devices. It's analogous to L2Arc for ZFS,
but Bcache also does writeback caching (besides just write through
caching), and it's filesystem agnostic. ")
    (license gpl2)))