Both Buildroot (toolchainfile.cmake.in\misc\support - buildroot - Buildroot: Making Embedded Linux easy) and OpenEmbedded/Yocto Project (openembedded-core/OEToolchainConfig.cmake at master · openembedded/openembedded-core · GitHub) do it. But in their cases it looks like they started using CMAKE_FIND_ROOT_PATH, they later added CMAKE_SYSROOT and forgot(?) to remove CMAKE_FIND_ROOT_PATH.
In the case of Android NDK an issue was reported (NDK cmake toolchain overrides CMAKE_FIND_ROOT_PATH · Issue #912 · android/ndk · GitHub) and then fixed by keep touching CMAKE_FIND_ROOT_PATH, but only appending to it.