binutils: replace hard-links with soft-links to fix rpath

binutils: replace hard-links with soft-links to fix rpath

binutils installs its binaries both as bin/<tuple>-<tool> and as
<tuple>/bin/<tool>, and hardlinks are used to reduce disk space
consumption. This causes a problem for host-binutils with our rpath
fixing logic done by "make sdk".

Indeed, the fix-rpath script starts by fixing up the rpath of
bin/<tuple>-<tool>, and sets the RPATH to $ORIGIN/../lib/. Then
fix-rpath moves on to <tuple>/bin/<tool>, and doesn't find the library
the tool depends on, and clears the RPATH. The result is that the
binutils tool are not usable.

Note that this is only visible currently on the ARC architecture,
because on this architecture, binutils is fetched from git, which
causes host-flex to be built, and some binutils tools to use the libfl
shared library. Therefore, the binutils tools don't use just the
standard C library (which is provided by the system) but also libfl
from $(HOST_DIR)/lib, and therefore if the RPATH isn't set correctly,
those tools don't work properly.

In order to address this, this comit adds a post-install hook to
host-binutils that replaces those hard links by symbolic links. It is
worth mentioning that library loading and RPATH usage occurs *after*
resolving the symbolic links, which makes this solution work.

Fixes:

  http://autobuild.buildroot.net/results/b2562b05d397d4e1ffe0f8d2f4ce4c84ab6feae1/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>