From GCC's standpoint ARC's multilib items are defined by "mcpu" values
which we have quite a few and for all of them might be built optimized
cross-toolchain.
From Glibc's standpoint multilib is just multi-ABI [1] and so very limited
versions are supposed to co-exist (e.g. arc700 & archs).
Here we force Glibc to install libraries in GCC's multilib folder to create
a universal cross-toolchain that has libs optimized for multiple CPU types.
But note we only need to mess with installation paths in case of real
multilib, otherwise we keep default "lib/" paths so that GCC finds default
(the one and only) libs where it expects them to be.
Also here we add a sample which allows to build universal Glibc Linux
toolchain for ARC.
[1] https://sourceware.org/ml/libc-alpha/2019-06/msg00018.html
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
