[3.21] main/glib: use portable code to suppress part of trigger output

this is what I wanted to do, but didn't figure out how to, thank you @nbuwe for the example code

it also looks like the hack I had will fail with dash-binsh and yash-binsh, regardless of the if-statement checking for busybox-binsh

since I'm fairly confident this fixes the breakage I introduced with !72173 (merged), I have merged this to edge with !76731 (merged), but I will leave this open for review before it goes into 3.21-stable