package/patchelf: new host package

In some situations, users may want to tweak the dynamic section of the
binaries (for example to add/set the RPATH to $ORIGIN/../lib).

Because it is not trivial to do it properly from the Buildroot
infrastructure, allow those users to use patchelf (e.g. from a
post-build script) to tweak binaries.

patchelf is able to:
  - modify an existing DT_RUNPATH tags
  - add a DT_RUNPATH tag if not already present
  - do the above to the DT_RPATH tag, too
  - set the path to the interpreter
  - remove DT_NEEDED tags
  - query a binary for the DT_RUNPATH/DT_RPATH tag, or for the
    interpreter path

Does not really fix #7172, but this is an appropriate workaround.

[Thomas: change license to GPLv3+, as mentionned in the project's
README file.]

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Mike Zick <minimod@morethan.org>
Reviewed-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>