Readline multiline completer #1573

Job	Run time
Build slim tarball	1m 35s
aarch64-linux: with shared libraries	2h 25m 30s
x86_64-linux: with shared libraries	2h 27m 44s
aarch64-darwin: with shared libraries	2h 18m 25s
x86_64-darwin: with shared libraries	3h 6m 34s
	10h 19m 48s

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