[OpenMP] Add a flag for embedding a file into the module

This patch adds support for a flag `-fembed-offload-binary` to embed a
file as an ELF section in the output by placing it in a global variable.
This can be used to bundle offloading files with the host binary so it
can be accessed by the linker. The section is named using the
`-fembed-offload-section` option.

Depends on D116541

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D116542