Meson

nixd/Syntax: add legacy let warning #1573

Job	Run time
nix-build-develop-clang (none, release, true)	2m 3s
nix-build-develop-gcc (none, release, true)	2m 21s
nix-build-develop-clang (none, release, false)	2m 54s
nix-build-develop-gcc (none, release, false)	2m 32s
nix-build-develop-clang (none, debug, true)	2m 0s
nix-build-develop-gcc (none, debug, true)	2m 2s
nix-build-develop-clang (none, debug, false)	2m 27s
nix-build-develop-gcc (none, debug, false)	1m 58s
nix-build-develop-gcc (undefined, release, true)	3m 55s
nix-build-develop-gcc (undefined, release, false)	3m 18s
nix-build-develop-gcc (undefined, debug, true)	2m 4s
nix-build-develop-gcc (undefined, debug, false)	2m 23s
	29m 57s

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