build: Preserve stderr for shell tests.

Fixes a regression introduced in
a9edb211e7 where the .log files of the .sh
tests would not contain stderr.

* build-aux/test-env.in: Redirect stderr only when --quiet-stderr is
passed.
* Makefile.am (SCM_LOG_DRIVER): Add --quiet-stderr.

Makefile.am

@@ -297,8 +297,11 @@ TESTS = $(SCM_TESTS) $(SH_TESTS)
 
 AM_TESTS_ENVIRONMENT = abs_top_srcdir="$(abs_top_srcdir)" GUILE_AUTO_COMPILE=0
 
-SCM_LOG_DRIVER = $(top_builddir)/test-env $(GUILE) --no-auto-compile \
-                   -e main $(top_srcdir)/build-aux/test-driver.scm
+SCM_LOG_DRIVER =				\
+  $(top_builddir)/test-env --quiet-stderr	\
+  $(GUILE) --no-auto-compile -e main		\
+      $(top_srcdir)/build-aux/test-driver.scm
+
 AM_SCM_LOG_DRIVER_FLAGS = --brief=yes
 
 SH_LOG_COMPILER = $(top_builddir)/test-env $(SHELL)

build-aux/test-env.in

@@ -29,12 +29,18 @@
 # stdout.
 unset CDPATH
 
+case "$1" in
+    --quiet-stderr)
+	# Silence the daemon's output, which is often useless, as well as that
+	# of Bash (such as "Terminated" messages when 'guix-daemon' is
+	# killed.)
+	exec 2> /dev/null
+	shift
+	;;
+esac
+
 if [ -x "@abs_top_builddir@/guix-daemon" ]
 then
-    # Silence the daemon's output, which is often useless, as well as that of
-    # Bash (such as "Terminated" messages when 'guix-daemon' is killed.)
-    exec 2> /dev/null
-
     NIX_STORE_DIR="@GUIX_TEST_ROOT@/store"
 
     # Do that because store.scm calls `canonicalize-path' on it.