classes/toolchain/clang: Add placeholder for dynamic linker in cross-canadian packages

classes/toolchain/clang: Add placeholder for dynamic linker in cross-canadian packages

clang-cross-canadian is just symlinking into nativesdk-clang unlike gcc which
has separate binaries and they have inbuilt dynamic linker specs. To help clang
built cross-canadian binaries add it via cmdline option here, cross-canadian
binaries are only usable on installed SDKs, and these paths get re-written with
correct SDK specific linker during SDK install relocation process.

This helps clang built cross-canadian tools e.g. from binutils-cross-canadian
be relocated correctly on SDK install.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>