Specifying a CMake toolchain file prevented host/createconf from being created

When I specify a `CMAKE_TOOLCHAIN_FILE` for my aarch64le target, the `host/confdir/createconf` build that occurs during the configure step targets the target instead of the host.

To get around this I have to do two builds.

I'm not sure what the best solution is. I suspect though that maybe creating a `CMAKE_HOST_TOOLCHAIN_FILE:FILEPATH` cache variable, and then injecting it into the `execute_command` code as a `CMAKE_TOOLCHAIN_FILE` _might_ fix it. I say _might_ because toolchains are a little special in CMake.