test-setup.sh: Attempt to raise the original signal once more

On POSIX-like systems, processes may either terminate normally with an
integer exit code. The exit code may span the full range of int, even
though all but the waitid() function retur the bottom eight bits. In
addition to that, processes may terminate abnormally due to a signal
(SIGABRT, SIGSEGV, etc.)

POSIX shells (sh, bash, etc.) are more restrictive, in that they can
only return exit codes between 0 and 126. 127 is used to denote that the
executable cannot be found. Exit codes above 128 indicate that the
process terminated due to a signal.

Right now we let test-setup.sh terminate using the exit code obtained
using $?. This means that if a program terminates due to SIGABRT,
test-setup.sh terminates with exit code 128+6=134. This causes us to
lose some information, as the (remote) execution environment now only
sees plain exit codes.

This change extends test-setup.sh to check for exit codes above 128. In
that case it will send a signal to itself, so that the original signal
condition is raised once again.

See also: bazelbuild/remote-apis#240

tools/test/test-setup.sh

@@ -432,4 +432,8 @@ if [[ -n "$TEST_UNDECLARED_OUTPUTS_ZIP" ]] && cd "$TEST_UNDECLARED_OUTPUTS_DIR";
   fi
 fi
 
+# Raise the original signal if the test terminated abnormally.
+if [ $exitCode -gt 128 ]; then
+  kill -$(($exitCode - 128)) $$ &> /dev/null
+fi
 exit $exitCode