environment: Correctly handle abnormal exits.

Fixes <http://bugs.gnu.org/21958>.

* guix/scripts/environment.scm (status->exit-code): New procedure.
(exit/status, primitive-exit/status): Use it.
* tests/guix-environment-container.sh: Add test.

guix/scripts/environment.scm

@@ -317,8 +317,15 @@ requisite store items i.e. the union closure of all the inputs."
                                       (map input->requisites inputs))))
     (return (delete-duplicates (concatenate reqs)))))
 
-(define exit/status (compose exit status:exit-val))
-(define primitive-exit/status (compose primitive-exit status:exit-val))
+(define (status->exit-code status)
+  "Compute the exit code made from STATUS, a value as returned by 'waitpid',
+and suitable for 'exit'."
+  ;; See <bits/waitstatus.h>.
+  (or (status:exit-val status)
+      (logior #x80 (status:term-sig status))))
+
+(define exit/status (compose exit status->exit-code))
+(define primitive-exit/status (compose primitive-exit status->exit-code))
 
 (define (launch-environment command inputs paths pure?)
   "Run COMMAND in a new environment containing INPUTS, using the native search

tests/guix-environment-container.sh

@@ -81,3 +81,10 @@ grep $(guix build guile-bootstrap) $tmpdir/mounts
 grep -e "$NIX_STORE_DIR/.*-bash" $tmpdir/mounts # bootstrap bash
 
 rm $tmpdir/mounts
+
+if guix environment --bootstrap --container \
+	--ad-hoc bootstrap-binaries -- kill -SEGV 2
+then false;
+else
+    test $? -gt 127
+fi