* ci.yml: Execute llvm-mt in build-msys2. #207

Job	Run time
build-msys2	9m 44s
build-freebsd (FreeBSD/amd64 14.2 with ports)	5m 20s
build-macos (macos-latest)	1m 52s
build-linux (ubuntu:latest)	5m 50s
build-netbsd (NetBSD/amd64 10.1 with pkgsrc)	8m 22s
build-macos (macos-13)	3m 21s
build-linux (ubuntu:22.04)	5m 17s
build-linux (debian:12)	6m 12s
build-linux (debian:11)	5m 39s
build-linux (archlinux:base)	6m 30s
	58m 7s

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