$(AS) was never used: $(assemble) invokes the C compiler instead.
In case of LLVM, this will allow us to consistently use the LLVM
internal assembler for both inline assembly in C and assembly
sources; so, avoid ever invoking binutils as explicitly.

`ranlib` is not necessary on any system we can possibly build for,
as it is superseded by `ar s` for the last ten years or so (at least).
Thus, change ar invocations to `ar crs`, also removing a `l` flag
that is ignored by binutils.