Function get_llvm_build_status 

pub fn get_llvm_build_status(
    builder: &Builder<'_>,
    target: TargetSelection,
) -> LlvmBuildStatus

This returns whether we’ve already previously built LLVM.

This will return the llvm-config if it can get it (but it will not build it if not).

Note that calling this function might checkout the LLVM submodule!