Rewrite accel-derive with rust-ptx-linker

[termoshtt]

Rewrite nvptx and accel-derive (i.e. reject re-merging nvptx rust-accel/nvptx#16)

Use libcore in rustup

libcore, liballoc, and libstd is in rustup distribution even in stable https://github.com/rust-lang/rust/blob/master/src/librustc_target/spec/nvptx64_nvidia_cuda.rs

Status of rust-ptx-linker

• rustc-llvm-proxy does not works well both on Linux and Windows.
• rust-ptx-linker works without llvm-proxy features, which is default and enables rustc-llvm-proxy.
• Should we consider to distribute rust-ptx-linker with statically linked LLVM?
• Anyway, accel-derive should be rewriten to use rust-ptx-linker Can Accel use the ptx-linker? #54

Rust -> PTX without creating crate

As described in #61. In current way, one #[kernel] creates a crate on /tmp and compile them. It can be heavy.