meson: don't try to guess versioned clang/llvm-strip bins for cross compile
    
    This should simplify overriding the program locations as the binary
    names should now not change if cross compiling.
    
    It's likely any attempts at autodetecting these in cross environments will
    be brittle at best so lets just disable it.
    
    (cherry picked from commit 4b7b73c7140b3c923064c6bf27a30b0e88a72f7a)