ARC: Update relocation syntax for old-thread model code

ARC: Update relocation syntax for old-thread model code

This commit reverses a change introduced in commit 20554a78a9bba that
split some of the ARC code into two based on whether uClibc was
configured with native threads or not.

The native thread code was updated to use the relocation syntax of
modern binutils, while the non-native code path used a syntax only
accepted in older versions of binutils.

The problem with this is that the choice of old binutils or not is
orthogonal to the choice of native threads or not, and so, inevitably a
user with a recent version of binutils can make the choice to configure
uClibc with non-native thread support, and run into code that will not
assemble.

The solution is either to abandon support for the old tools completely,
or to add a new compile time flag for ARC that is set when the version
of binutils being used is old; this new flag would allow the old
relocation structure to be selected.

In this commit I have simply dropped support for older versions of the
tools.