Embed/wrap lld linker

[jpsamaroo]

Currently we invoke ld.lld manually to link our kernel's .o file into the final executable. We should figure out how to embed lld (or call the appropriate C++ functions in LLVM) so that we don't rely on the lld binary existing on the user's system.

[vchuravy]

Julia currently doesn't ship ldd, but luckily HSA only really supports Linux, so we can assume that we have a linker available.

[jpsamaroo]

We should pull in LLVM_full_jll if possible, it seems like that has a working ld.lld.