Shrink size of platform tag enum #855

Job	Run time
macos-x86_64	4m 10s
sdist	6m 18s
macos-aarch64	4m 48s
linux (x86_64-unknown-linux-gnu)	5m 49s
linux (i686-unknown-linux-gnu)	5m 50s
linux-arm (aarch64-unknown-linux-gnu, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	6m 8s
windows (x86_64-pc-windows-msvc, x64)	6m 10s
linux-arm (armv7-unknown-linux-gnueabihf, armv7)	6m 6s
windows (i686-pc-windows-msvc, x86)	6m 10s
linux-powerpc (powerpc64le-unknown-linux-gnu, ppc64le, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	6m 7s
linux-s390x (s390x-unknown-linux-gnu, s390x)	5m 48s
linux-arm (arm-unknown-linux-musleabihf, arm)	6m 7s
linux-powerpc (powerpc64-unknown-linux-gnu, ppc64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	6m 8s
musllinux (x86_64-unknown-linux-musl)	6m 7s
musllinux-cross (aarch64-unknown-linux-musl, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	6m 7s
musllinux (i686-unknown-linux-musl)	6m 8s
musllinux-cross (armv7-unknown-linux-musleabihf, armv7)	6m 6s
	1h 40m 7s

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