Allow linking alternate memory management implementations (#454) #689

Job	Run time
macos-12 (CMake) (LLVM)	10m 36s
debian:12 (Latest Mapnik) (CMake) (GNU)	3m 47s
macos-13 (CMake) (LLVM)	12m 42s
freebsd13 (CMake) (LLVM)	9m 3s
ubuntu:24.04 (Latest Mapnik) (CMake) (GNU)	3m 50s
macos-14 (CMake) (LLVM)	9m 28s
debian:11 (CMake) (GNU)	3m 28s
freebsd14 (CMake) (LLVM)	8m 36s
debian:12 (CMake) (GNU)	3m 34s
fedora:39 (CMake) (GNU)	4m 10s
fedora:40 (CMake) (GNU)	7m 15s
opensuse/leap:15 (CMake) (GNU)	4m 57s
quay.io/centos/centos:stream9 (CMake) (GNU)	4m 8s
ubuntu:22.04 (CMake) (GNU)	3m 18s
debian:unstable (CMake) (GNU)	3m 14s
fedora:rawhide (CMake) (GNU)	3m 45s
ubuntu:devel (CMake) (GNU)	3m 18s
ubuntu:24.04 (Autotools) (GNU)	2m 27s
ubuntu:24.04 (Autotools) (LLVM)	2m 37s
ubuntu:24.04 (CMake) (GNU)	3m 18s
ubuntu:24.04 (CMake) (LLVM)	3m 31s
	1h 51m 2s

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