cmake: exclude platform sources #145

Job	Run time
macosx	1m 0s
linux - debian:bookworm	1m 44s
linux - arm32v7/debian:bookworm	15m 4s
linux - archlinux - amd64	57s
linux - archlinux - arm64	2m 32s
linux - arm64v8/debian:bookworm	3m 1s
android	4m 8s
ios	1m 17s
linux - ubuntu:noble	1m 40s
linux - igagis/raspbian:bookworm	10m 45s
msvs	4m 34s
conan - linux \|	1m 53s
msys2 - mingw32	1m 58s
conan - linux \| arm32	12m 18s
msys2 - mingw64	2m 37s
conan - linux \| arm64	3m 19s
conan - macos-12	15m 18s
vcpkg - linux \|	1m 31s
	1h 25m 36s

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