[clang-offload-bundler] Standardize TargetID field for bundler

The bundler accepts both of the following for the --target option:
  hip-amdgcn-amd-amdhsa-gfx900    (no env field)
  hip-amdgcn-amd-amdhsa--gfx900   (blank env field)

The environment field is defined as optional for Triples
in Triple.h. However, in this patch we update the bundler to
internally standardize to include the env field. While users
aren't required to specify an env field when listing targets on
the commandline, bundles generated by the offload-bundler will
include the ABI field.

This standardization simplifies things for APIs that deal with
bundles generated by the clang-offload-bundler tool.

Differential Revision: https://reviews.llvm.org/D145770