gcc: provide both native and cross forms of gcc.libs libraries

I would like to use --sysroot=/nix/store/does/not/exist hack
for both `gcc` and `clang` drivers to remove default include
(and library) search paths when we override them with libc.

For `gcc` it works as is. But for `clang` it also drops some of
`gcc` search paths`. Let'sconsider 2 lookups.

Successful lookup (no `--sysroot`):

    $ printf "int main(){}" | clang++ -x c++ - -Wl,--verbose |& grep -F stdc++
    attempt to open /nix/store/...-gcc-11.3.0/lib/gcc/x86_64-unknown-linux-gnu/11.3.0/libstdc++.so failed
    attempt to open /nix/store/...-gcc-11.3.0-lib/x86_64-unknown-linux-gnu/lib/libstdc++.so failed
    attempt to open /nix/store/...-clang-11.1.0-lib/lib/libstdc++.so failed
    attempt to open /nix/store/...-gcc-11.3.0/lib64/gcc/x86_64-unknown-linux-gnu/11.3.0/libstdc++.so failed
    attempt to open /nix/store/...-gcc-11.3.0/lib64/gcc/x86_64-unknown-linux-gnu/11.3.0/../../../../lib64/libstdc++.so failed
    /nix/store/...-gcc-11.3.0/lib64/gcc/x86_64-unknown-linux-gnu/11.3.0/../../../../lib64/libstdc++.a

Failed lookup (has `--sysroot`):

    $ printf "int main(){}" | clang++ --sysroot=/does/not/exist -x c++ - -Wl,--verbose |& grep -F stdc++
    attempt to open /nix/store/...-gcc-11.3.0/lib/gcc/x86_64-unknown-linux-gnu/11.3.0/libstdc++.so failed
    attempt to open /nix/store/...-gcc-11.3.0-lib/x86_64-unknown-linux-gnu/lib/libstdc++.so failed
    attempt to open /nix/store/...-clang-11.1.0-lib/lib/libstdc++.so failed
    attempt to open /nix/store/...-gcc-11.3.0/lib64/gcc/x86_64-unknown-linux-gnu/11.3.0/libstdc++.so failed
    /nix/store/...-binutils-2.39/bin/ld: cannot find -lstdc++: No such file or directory

Note how `clang` starts the search roughly from
`gcc-11.3.0-lib/x86_64-unknown-linux-gnu/lib` in both cases. I think
it's our preferred location for both native and cross cases.

The change adds such a symlink:

    `gcc-11.3.0-lib` -> `gcc-11.3.0-lib/x86_64-unknown-linux-gnu`

0 files changed, 0 insertions, 0 deletions