ci: Run 'time' in the background and propagate signals to test process

Simply exec'ing time didn't produce any output from it when a test
timed out.

Fixes: 35f59e14f8 "ci: Use GNU time as meson test wrapper"
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8830>

.gitlab-ci.yml

@@ -277,7 +277,7 @@ x86_build:
   extends:
     - .use-x86_build-base
   variables:
-    MESA_IMAGE_TAG: &x86_build "2021-01-29-time"
+    MESA_IMAGE_TAG: &x86_build "2021-02-02-procps"
 
 .use-x86_build:
   variables:

.gitlab-ci/container/x86_build.sh

@@ -32,6 +32,7 @@ apt-get install -y --no-remove \
       liblua5.3-dev \
       libxml2-dev \
       ocl-icd-opencl-dev \
+      procps \
       time \
       wine-development \
       wine32-development

.gitlab-ci/meson/test-wrapper.sh

@@ -1,8 +1,24 @@
 #!/bin/sh
 
 # Only use GNU time if available, not any shell built-in command
-if test -f /usr/bin/time; then
-    exec /usr/bin/time -v "$@"
+if ! test -f /usr/bin/time; then
+    exec "$@"
 fi
 
-exec "$@"
+
+# If the test times out, meson sends SIGINT & SIGTERM signals to this process.
+# Simply exec'ing "time" would result in no output from that in this case.
+# Instead, we need to run "time" in the background, catch the signals and
+# propagate them to the actual test process.
+
+/usr/bin/time -v "$@" &
+TIMEPID=$!
+TESTPID=$(ps --ppid $TIMEPID -o pid=)
+
+if test "x$TESTPID" != x; then
+    trap 'kill -INT $TESTPID; wait $TIMEPID; exit $?' INT
+    trap 'kill -TERM $TESTPID; wait $TIMEPID; exit $?' TERM
+fi
+
+wait $TIMEPID
+exit $?