Commit: Do not build libctf for non-ELF targets

[Nix]

On 29 May 2019, Nick Clifton said:

> Hi Guys,
>
>   I just noticed this morning that the new libctf library does not build
>   for non-ELF based targets.  So I am applying the patch below to fix
>   this issue.  Ideally I would like a better way to detect non-ELF
>   targets, but for now I am using just a simple list of known triples.

We just pushed a fix that arranges that it *does* build on non-ELF
targets with nearly full capabilities (all you lose is the ability to
automatically associate the ELF string and symbol tables with a
newly-opened CTF file, which isn't meaningful on non-ELF anyway), which
means that objdump and readelf keep working with CTF support even on
non-ELF and don't need to change at all. So you can probably revert this
one :)

(btw, the method I used to discern ELFness was stolen from GDB: an
AC_TRY_LINK() against the bfd_*_elf_*() function causing the trouble,
and associated LIBS/LDFLAGS/CFLAGS adjustments and dep changes so we
don't configure libctf before libbfd has finished building.)

-- 
NULL && (void)