Here's a hackish way to do it for the pipeline /bin/true |sleep 60 (nonsensical, but easy to kill -INT)...

system("/bin/true |sleep 60; kill -`expr \$? / 64` \$\$");
print "sysret: $?\n";
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The shell runs the pipeline, calculates what signal the process died from, and kills itself with that signal. If the process didn't die from a signal, it kills itself with signal 0, which does nothing.