gnu: go-1.13: Target aarch64-linux for aarch64-linux.

Fixes <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=34872>.

* gnu/packages/golang.scm (go-1.13)[arguments]: Set system to
aarch64-linux when building for aarch64-linux. Adjust 'prebuild phase
to skip tests which fail on aarch64-linux.

gnu/packages/golang.scm

@@ -233,6 +233,11 @@ (define-public go-1.13
          "07gksk9194wa90xyd6yhagxfv7syvsx29bh8ypc4mg700vc1kfrl"))))
     (arguments
      (substitute-keyword-arguments (package-arguments go-1.4)
+       ((#:system system)
+        (if (string-prefix? "aarch64-linux" (or (%current-system)
+                                                (%current-target-system)))
+          "aarch64-linux"
+          system))
        ((#:phases phases)
         `(modify-phases ,phases
            (replace 'prebuild
@@ -329,6 +334,10 @@ (define-public go-1.13
                     ("syscall/exec_linux_test.go"
                      "(.+)(TestCloneNEWUSERAndRemapNoRootDisableSetgroups.+)")))
 
+                 ;; These tests fail on aarch64-linux
+                 (substitute* "cmd/dist/test.go"
+                   (("t.registerHostTest\\(\"testsanitizers/msan.*") ""))
+
                  ;; fix shebang for testar script
                  ;; note the target script is generated at build time.
                  (substitute* "../misc/cgo/testcarchive/carchive_test.go"