[clang-offload-bundler] Add unbundling of archives containing bundled object...

[clang-offload-bundler] Add unbundling of archives containing bundled object files into device specific archives

This patch adds unbundling support of an archive file. It takes an
archive file along with a set of offload targets as input.
Output is a device specific archive for each given offload target.
Input archive contains bundled code objects bundled using
clang-offload-bundler. Each generated device specific archive contains
a set of device code object files which are named as
<Parent Bundle Name>-<CodeObject-GPUArch>.

Entries in input archive can be of any binary type which is
supported by clang-offload-bundler, like *.bc. Output archives will
contain files in same type.

Example Usuage:
  clang-offload-bundler --unbundle --inputs=lib-generic.a -type=a
      -targets=openmp-amdgcn-amdhsa--gfx906,openmp-amdgcn-amdhsa--gfx908
      -outputs=devicelib-gfx906.a,deviceLib-gfx908.a

Reviewed By: jdoerfert, yaxunl

Differential Revision: https://reviews.llvm.org/D93525