binutils/readelf: build against msgpack, dump NT_AMDGPU_METADATA note contents

binutils/readelf: build against msgpack, dump NT_AMDGPU_METADATA note contents

The AMDGPU HSA OS ABI (code object v3 and above) defines the
NT_AMDGPU_METADATA ELF note [1].  The content is a msgpack object
describing, among other things, the kernels present in the code object
and how to call them.

I think it would be useful for readelf to be able to display the content
of those notes.  msgpack is a structured format, a bit like JSON, except
not text-based.  It is therefore possible to dump the contents in
human-readable form without knowledge of the specific layout of the
note.

Add configury to binutils to optionally check for the msgpack C library
[2].  Add There is a new --with{,out}-msgpack configure flag, and the actual
library lookup is done using pkg-config.

If msgpack support is enabled, dumping a NT_AMDGPU_METADATA note looks
like:

    $ readelf --notes amdgpu-code-object
    Displaying notes found in: .note
      Owner                Data size        Description
      AMDGPU               0x0000040d       NT_AMDGPU_METADATA (code object metadata)
        {
          "amdhsa.kernels": [
            {
              ".args": [
                {
                  ".address_space": "global",
                  ".name": "out.coerce",
                  ".offset": 0,
                  ".size": 8,
                  ".value_kind": "global_buffer",
                },
      <snip>

If msgpack support is disabled, dump the contents as hex, as is done
with notes that are not handled in a special way.  This allows one to
decode the contents manually (maybe using a command-line msgpack
decoder) if really needed.

[1] https://llvm.org/docs/AMDGPUUsage.html#code-object-metadata
[2] https://github.com/msgpack/msgpack-c/tree/c_master

binutils/ChangeLog:

	* Makefile.am (readelf_CFLAGS): New.
	(readelf_LDADD): Add MSGPACK_LIBS.
	* Makefile.in: Re-generate.
	* config.in: Re-generate.
	* configure: Re-generate.
	* configure.ac: Add --with-msgpack flag and check for msgpack
	using pkg-config.
	* readelf.c: Include msgpack.h if HAVE_MSGPACK.
	(print_note_contents_hex): New.
	(print_indents): New.
	(dump_msgpack_obj): New.
	(dump_msgpack): New.
	(print_amdgpu_note): New.
	(process_note): Handle NT_AMDGPU_METADATA note contents.
	Use print_note_contents_hex.

Change-Id: Ia60a654e620bc32dfdb1bccd845594e2af328b84