mv constexpr def into if #84

Job	Run time
Release linux x86_64 static	3m 31s
.deb packages / ubuntu:22.04	5m 51s
Windows Build (vcpkg / x86-windows-static)	4m 18s
Windows Build (vcpkg / x64-windows-static)	4m 33s
Windows Build (vcpkg / x86-windows)	2m 55s
.deb packages / ubuntu:20.04	5m 40s
Windows Build (vcpkg / x64-windows)	2m 54s
.deb packages / debian:bullseye	5m 16s
.deb packages / debian:bookworm	5m 19s
.deb packages / debian:trixie	1m 23s
.deb packages / debian:sid	5m 13s
	46m 53s

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