utils: Define 'target-hurd?' predicate.

It behaves similarily to the other target-...? procedures.
The usage of hurd-triplet? / target-hurd? in libgc appears
incorrect to me, as (%current-system) is normally never false.

* gnu/packages/hurd.scm (hurd-triplet?): Move to ...
* guix/util.scm (target-hurd?): ... here, let its argument
  default to (%current-target-system) or (%current-system),
  and write a docstring.
* gnu/packages/hurd.scm
  (hurd-target?, hurd-system?): Use target-hurd? instead of
  hurd-triplet?.
* gnu/packages/bdw-gc.scm (libgc): Likewise.
* gnu/packages/cross-base.scm
  (cross-libc)[arguments]<#:configure-flags>: Likewise.
  (cross-libc)[arguments]<#:phases>: Likewise.
  (cross-libc)[arguments]<#:native-inputs>: Likewise.
* gnu/packages/make-boostrap.scm
  (%glibc-stripped)[inputs]: Likewise.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

gnu/packages/bdw-gc.scm

@@ -56,7 +56,7 @@
        ;; to configure script. See bug report and discussion:
        ;; <https://lists.opendylan.org/pipermail/bdwgc/2017-April/006275.html>
        ;; <https://lists.gnu.org/archive/html/bug-hurd/2017-01/msg00008.html>
-       ,@(if (hurd-triplet? (or (%current-system)
+       ,@(if (target-hurd? (or (%current-system)
                                (%current-target-system)))
              '("--disable-gcj-support")
              '()))))

gnu/packages/cross-base.scm

@@ -505,7 +505,7 @@ and the cross tool chain."
                ,@(package-arguments libc))
            ((#:configure-flags flags)
             `(cons ,(string-append "--host=" target)
-                   ,(if (hurd-triplet? target)
+                   ,(if (target-hurd? target)
                         `(cons "--disable-werror" ,flags)
                         flags)))
            ((#:phases phases)
@@ -519,7 +519,7 @@ and the cross tool chain."
                      (setenv "CROSS_LIBRARY_PATH"
                              (string-append kernel "/lib")) ; for Hurd's libihash
                      #t)))
-               ,@(if (hurd-triplet? target)
+               ,@(if (target-hurd? target)
                      '((add-after 'install 'augment-libc.so
                          (lambda* (#:key outputs #:allow-other-keys)
                            (let* ((out (assoc-ref outputs "out")))
@@ -536,7 +536,7 @@ and the cross tool chain."
 
         (native-inputs `(("cross-gcc" ,xgcc)
                          ("cross-binutils" ,xbinutils)
-                         ,@(if (hurd-triplet? target)
+                         ,@(if (target-hurd? target)
                                `(("cross-mig"
                                   ,@(assoc-ref (package-native-inputs xheaders)
                                                "cross-mig")))

gnu/packages/hurd.scm

@@ -51,20 +51,16 @@
             hurd-target?
             hurd-triplet?))
 
-(define (hurd-triplet? triplet)
-  (and (string-suffix? "-gnu" triplet)
-       (not (string-contains triplet "linux"))))
-
 (define (hurd-target?)
   "Return true if the cross-compilation target or the current system is
 GNU/Hurd."
-  (or (and=> (%current-target-system) hurd-triplet?)
+  (or (and=> (%current-target-system) target-hurd?)
       (and (not (%current-target-system))
-           (and=> (%current-system) hurd-triplet?))))
+           (and=> (%current-system) target-hurd?))))
 
 (define (hurd-system?)
   "Return true if the current system is the Hurd."
-  (and=> (%current-system) hurd-triplet?))
+  (and=> (%current-system) target-hurd?))
 
 (define (hurd-source-url version)
   (string-append "mirror://gnu/hurd/hurd-"

gnu/packages/make-bootstrap.scm

@@ -439,7 +439,7 @@ for `sh' in $PATH, and without nscd, and with static NSS modules."
                                (assoc-ref %build-inputs "kernel-headers")))))
       (inputs `(("kernel-headers"
                  ,(if (or (and (%current-target-system)
-                               (hurd-triplet? (%current-target-system)))
+                               (target-hurd? (%current-target-system)))
                           (string-suffix? "-hurd" (%current-system)))
                       gnumach-headers
                       linux-libre-headers))

guix/utils.scm

@@ -85,6 +85,7 @@
             %current-target-system
             package-name->name+version
             target-linux?
+            target-hurd?
             target-mingw?
             target-arm32?
             target-aarch64?
@@ -639,6 +640,12 @@ a character other than '@'."
   "Does the operating system of TARGET use the Linux kernel?"
   (->bool (string-contains target "linux")))
 
+(define* (target-hurd? #:optional (target (or (%current-target-system)
+                                              (%current-system))))
+  "Does TARGET represent the GNU(/Hurd) system?"
+  (and (string-suffix? "-gnu" target)
+       (not (string-contains target "linux"))))
+
 (define* (target-mingw? #:optional (target (%current-target-system)))
   (and target
        (string-suffix? "-mingw32" target)))