llext: fix undefined symbols #20666

Job	Run time
LP64-WIP	4m 19s
manifest-check	43s
build-windows (imx8 imx8x imx8m imx8ulp)	8m 35s
build-windows (ptl)	6m 21s
build-windows (tgl tgl-h)	6m 36s
build-windows (mtl lnl)	7m 5s
build-windows (-d, lnl)	6m 17s
build-linux (mnfst, tgl tgl-h)	5m 40s
build-linux (mnfst, ptl)	5m 22s
build-linux (mnfst, imx8 imx8x imx8m imx8ulp)	6m 49s
build-linux (mnfst, mtl lnl)	6m 5s
build-linux (zmain, mtl lnl)	6m 29s
build-linux (zmain, imx8 imx8x imx8m imx8ulp)	7m 17s
build-linux (zmain, tgl tgl-h)	6m 7s
build-linux (zmain, ptl)	5m 17s
build-linux (-d, mnfst, lnl)	4m 42s
build-linux (mnfst, --all)	16m 26s
compare-linux-win	1m 19s
	1h 51m 29s

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