[LinkerWrapper] Use `clang` to perform the device linking

Right now in the linker wrapper we manually invoke a lot of the
toolchain programs. This reproduces a lot of logic that is already
handled in clang. Since D140158 we can now target all supported
toolchains directly via cross-compilation.

This patch changes the linker wrapper to consolidate all the alternate
linking and assembler steps into a generic call to `clang` and let clang
handle the argument handling. This heavily simplifies the interface.

Reviewed By: tra, JonChesterfield

Differential Revision: https://reviews.llvm.org/D142133