gnu: ld-wrapper-boot0: Work around strict evaluation of (%current-system).

Reported by Mark H Weaver <mhw@netris.org>
Partly fixes <http://bugs.gnu.org/24832>.

'ld-wrapper-boot0' was evaluating strictly instead of lazily, leading to
invalid system types.

* gnu/packages/base.scm (make-ld-wrapper): Turn #:target into a
one-argument procedure.  Honor it.
* gnu/packages/commencement.scm (ld-wrapper-boot0): Fix 'name' argument
to 'make-ld-wrapper'.  Make #:target argument a procedure.
* gnu/packages/cross-base.scm (cross-gcc): Adjust #:target argument.

gnu/packages/base.scm

@@ -422,14 +422,22 @@ included.")
    (license gpl3+)
    (home-page "http://www.gnu.org/software/binutils/")))
 
-(define* (make-ld-wrapper name #:key binutils
+(define* (make-ld-wrapper name #:key
+                          (target (const #f))
+                          binutils
                           (guile (canonical-package guile-2.0))
-                          (bash (canonical-package bash)) target
+                          (bash (canonical-package bash))
                           (guile-for-build guile))
   "Return a package called NAME that contains a wrapper for the 'ld' program
-of BINUTILS, which adds '-rpath' flags to the actual 'ld' command line.  When
-TARGET is not #f, make a wrapper for the cross-linker for TARGET, called
-'TARGET-ld'.  The wrapper uses GUILE and BASH."
+of BINUTILS, which adds '-rpath' flags to the actual 'ld' command line.  The
+wrapper uses GUILE and BASH.
+
+TARGET must be a one-argument procedure that, given a system type, returns a
+cross-compilation target triplet or #f.  When the result is not #f, make a
+wrapper for the cross-linker for that target, called 'TARGET-ld'."
+  ;; Note: #:system->target-triplet is a procedure so that the evaluation of
+  ;; its result can be delayed until the 'arguments' field is evaluated, thus
+  ;; in a context where '%current-system' is accurate.
   (package
     (name name)
     (version "0")
@@ -441,6 +449,7 @@ TARGET is not #f, make a wrapper for the cross-linker for TARGET, called
               ("wrapper"  ,(search-path %load-path
                                         "gnu/packages/ld-wrapper.in"))))
     (arguments
+     (let ((target (target (%current-system))))
        `(#:guile ,guile-for-build
          #:modules ((guix build utils))
          #:builder (begin
@@ -477,7 +486,7 @@ TARGET is not #f, make a wrapper for the cross-linker for TARGET, called
                                                              target "-ld")
                                               "/bin/ld"))))
                        (chmod ld #o555)
-                     (compile-file ld #:output-file go)))))
+                       (compile-file ld #:output-file go))))))
     (synopsis "The linker wrapper")
     (description
      "The linker wrapper (or 'ld-wrapper') wraps the linker to add any

gnu/packages/commencement.scm

@@ -424,8 +424,14 @@ the bootstrap environment."
 (define ld-wrapper-boot0
   ;; We need this so binaries on Hurd will have libmachuser and libhurduser
   ;; in their RUNPATH, otherwise validate-runpath will fail.
-  (make-ld-wrapper (string-append "ld-wrapper-" (boot-triplet))
-                   #:target (boot-triplet)
+  ;;
+  ;; XXX: Work around <http://bugs.gnu.org/24832> by fixing the name and
+  ;; triplet on GNU/Linux.  For GNU/Hurd, use the right triplet.
+  (make-ld-wrapper (string-append "ld-wrapper-" "x86_64-guix-linux-gnu")
+                   #:target (lambda (system)
+                              (if (string-suffix? "-linux" system)
+                                  "x86_64-guix-linux-gnu"
+                                  (boot-triplet system)))
                    #:binutils binutils-boot0
                    #:guile %bootstrap-guile
                    #:bash (car (assoc-ref %boot0-inputs "bash"))))

gnu/packages/cross-base.scm

@@ -254,7 +254,7 @@ GCC that does not target a libc; otherwise, target that libc."
     (native-inputs
      `(("ld-wrapper-cross" ,(make-ld-wrapper
                              (string-append "ld-wrapper-" target)
-                             #:target target
+                             #:target (const target)
                              #:binutils xbinutils))
        ("binutils-cross" ,xbinutils)