[clang-offload-wrapper] Add standard notes for ELF offload images

The patch adds ELF notes into SHT_NOTE sections of ELF offload images
passed to clang-offload-wrapper.

The new notes use a null-terminated "LLVMOMPOFFLOAD" note name.
There are currently three types of notes:

VERSION: a string (not null-terminated) representing the ELF offload
image structure. The current version '1.0' does not put any restrictions
on the structure of the image. If we ever need to come up with a common
structure for ELF offload images (e.g. to be able to analyze the images
in libomptarget in some standard way), then we will introduce new versions.

PRODUCER: a vendor specific name of the producing toolchain.
Upstream LLVM uses "LLVM" (not null-terminated).

PRODUCER_VERSION: a vendor specific version of the producing toolchain.
Upstream LLVM uses LLVM_VERSION_STRING with optional <space> LLVM_REVISION.

All three notes are not mandatory currently.

Differential Revision: https://reviews.llvm.org/D99551