bitbake.conf: add --enable-new-dtags to linker

bitbake.conf: add --enable-new-dtags to linker

Various versions of ld have different defaults for this
(even between e.g. Ubuntu 16.04 and 18.04). This has the
consequence of putting either RPATH or RUNPATH into the binary,
depending on the linker, which have different priorities
vs LD_LIBRARY_PATH env var. Also, I think, the original
executable binary is looked up for the tags when resolving
a dependency of a shared library when using RPATH, but not
RUNPATH.

Let's make this deterministic.

(From OE-Core rev: 661d700ab7428b0ad982bfd2714cca134bad85a2)

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>